Below, I've quoted his rules, and then added interpretations to suit AAO cases, as well as a few extra Ace Attorney-specific rules. Of course, they aren't absolute, and if you break them, it's not as if you'll suffer for it. Your players might, though.
Suggested addenda are appreciated!
The player has the right...
In an Ace Attorney case, if the player is to be penalized for presses, or only gets one shot at presenting a piece of evidence, they should be warned. A seemingly innocuous choice should not result in an instant game over!1. Not to be killed without warning.
At its most basic level, this means that a room with three exits, two of which lead to instant death and the third to treasure, is unreasonable without some hint.
Stakes should be proportional to situations. Throwing an insta-death penalty at the player somewhere early in the trial, in an otherwise casual situation, is nose-thumbing, not good design. Insta-death penalties in general should be reserved for dire situations.
In Ace Attorney, the biggest hints the player has are evidence and testimony statements, usually.2. Not to be given horribly unclear hints
Many years ago, I played a game in which going north from a cave led to a lethal pit. The hint was: there was a pride of lions carved above the doorway. Good hints can be skilfully hidden, or very brief (I think, for example, the hint in the moving-rocks plain problem in "Spellbreaker" is a masterpiece) but should not need explaining even after the event.
* Evidence should be clearly described; all relevant details should be accurate in the Court Record unless there is a very good reason for concealing them. The Court Record should always state the literal truth; even a false Autopsy Report is still a literal description of the contents of a falsified file.
* Contradictions should really be contradictions! If the wording of a statement does not actually create a contradiction with any evidence, asking someone to present evidence because it is "related" or "suggests some other possibility" is poor design. For example, if a witness says, "I went through the front door," pointing out the existence of unknown footprints at the back door is not even remotely a contradiction, even if it raises the possibility of a lie.
These can be combined into one rule:3. To be able to win without experience of past lives
Suppose, for instance, there is a nuclear bomb buried under some anonymous floor somewhere, which must be disarmed. It is unreasonable to expect a player to dig up this floor purely because in previous games, the bomb blew up there. To take a more concrete example, in "The Lurking Horror" there is something which needs cooking for the right length of time. As far as I can tell, the only way to find out the right time is by trial and error. But you only get one trial per game. In principle a good player should be able to play the entire game out without doing anything illogical. In similar vein:
4. To be able to win without knowledge of future events
For example, the game opens near a shop. You have one coin and can buy a lamp, a magic carpet or a periscope. Five minutes later you are transported away without warning to a submarine, whereupon you need a periscope. If you bought the carpet, bad luck.
A player-character should NEVER be required to act upon knowledge that they should not actually possess at that point in time, nor should they be required to "get lucky" based on the player's prior misfortunes!
Notice that every time the canonical games give you a chance to pick up one of two or three objects, only one of which is useful later, they also give you the chance to make the switch later.
The most obvious example here would be a cross-examination with penalties for pressing irrelevant statements in which it is only evidence in hindsight which statements were relevant.
----- I didn't do it ----
* I wasn't at the scene at all!
* I never touched the murder weapon!
* And I don't even know the victim!
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Pressing the first two statements results in severe penalties; pressing the third causes the witness to accidentally mention a personal fact about the victim. In hindsight, of course, only the third statement was relevant. But how on earth was the player supposed to know that before they got those giant penalties?! It's even worse in insta-death situations, especially when the game plays coy and makes it difficult to tell when you've made an incorrect choice.
I have seen equally dire examples even in good games. There is a final puzzle in one particularly high-profile fan game that involves a choice of evidence, the significance of which is only clear in hindsight, with a perfectly reasonable alternative solution not even being considered, and the wrong two choices leading into deceptive dead-ends (in which the attorney nonetheless proclaims the certainty of their answer)...
...but I'm not naming any names.
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Fortunately, the fan community seems to generally understand that the original games make sure you gather all the evidence for a reason. Unfortunately, this rule sometimes falls to the wayside where alternative endings are concerned. I don't mean that a player shouldn't be locked on a BAD END path for an obviously major choice, such as the wrong choice of culprit; that's a choice to make seriously and carefully.5. Not to have the game closed off without warning
Closed off meaning that it would become impossible to proceed at some later date. If there is a papier-mache wall which you can walk through at the very beginning of the game, it is extremely annoying to find that a puzzle at the very end requires it to still be intact, because every one of your saved games will be useless. Similarly it is quite common to have a room which can only be visited once per game. If there are two different things to be accomplished there, this should be hinted at.
I mean that locking a player out of the True Ending because of some issue that didn't seem to have monumental relevance at the time is goofy. Does it make players take the consequences of their actions seriously? Not if the actions were apparently minor! Visual novels are guilty of this sort of nonsense all the time (you walked left instead of right and not much happened except NO TRUE ENDING FOR YOU, IT IS HOPELESS), but that doesn't make it any less obnoxious to close off the path to victory.
Neither evidence presentations, movements during investigation, nor final answers to the crime should involve serious stretches of plausibility. The same applies to presses, and especially press-in-order puzzles. Is there any reason why a lawyer should "reset" what they've asked because of a conversation with their aide? Or why they should be forced to "lawnmower" through a testimony, pressing every statement or combination of statements repeatedly in an attempt to read the author's mind?6. Not to need to do unlikely things
For example, a game which depends on asking a policeman about something he could not reasonably know about. (Less extremely, the problem of the hacker's keys in "The Lurking Horror".) Another unlikely thing is waiting in uninteresting places. If you have a junction such that after five turns an elf turns up and gives you a magic ring, a player may well never spend five turns there and never solve what you intended to be straightforward. On the other hand, if you were to put something which demanded investigation in the junction, it might be fair enough. ("Zork III" is especially poor in this respect.)
Press-in-order puzzles are even worse when they demand that two statements be pressed consecutively. This is doubly goofy because real lawyers sometimes DO switch topics or stagger their questions during cross-examination in order to spring a trap!
Aside from "press-in-order", another example of an unlikely thing to do is a demand for multiple pieces of evidence with a VERY SPECIFIC combination required... when 2^X possible combinations of evidence would be reasonable, where X is the number of directly or indirectly relevant bits of evidence. Nothing kills a trial faster than a lousy multi-present or super-objection.
One of the worst offenders here is suspiciously similar to Nelson's example: a player (again in an otherwise good case) is expected to "wait around" during a cross-examination by clicking through it repeatedly. Again, I name no names.
Entire investigation sections are frequently "boring things for the sake of it." The event triggers that move an investigation along shouldn't be arbitrary, or a matter of walking through a bunch of random scenes examining random objects and presenting everything in the CR to people in the hope of finding the magic item.7. Not to need to do boring things for the sake of it
In the bad old days many games would make life difficult by putting objects needed to solve a problem miles away from where the problem was, despite all logic - say, putting a boat in the middle of a desert. Or, for example, it might be fun to have a four-discs tower of Hanoi puzzle in a game. But not an eight-discs one.
We don't need to do this. We really don't!
These rules obviously apply to text adventures. The first is about verbs, the second about nouns, and the third about the entire interface. The equivalent rule here is "be prepared to have the game recognize what the player is trying to do. And do not force the player to struggle to find the right way to express the right answer!" (Unless there's SOMEHOW a legitimate reason for that, which is rare.)8. Not to have to type exactly the right verb.
9. To be allowed reasonable synonyms.
10. To have a decent parser.
(explanation cut)
If two pieces of evidence can reasonably create a contradiction, write responses to both, even if one response is just, "No... I think another piece of evidence would work better here." Likewise, if two statements are contradicted, accept both, or rewrite the testimony to eliminate the ambiguity.
Canonical example: In Apollo Justice, you can present Alita Tiala's shoe (found in the Meraktis lobby) to show that she is connected to the Meraktis Clinic, but not the slipper containing her toe print with the word MERAKTIS written on it. This is sloppy.
One frequent complaint about AA games is their linearity. While this may be mostly unavoidable, what is less excusable is forcing the player to take a stupid action when a smart one should logically be available.11. To have reasonable freedom of action
Being locked up in a long sequence of prisons, with only brief escapes between them, is not all that entertaining. After a while the player begins to feel that the designer has tied him to a chair in order to shout the plot at him.
Worst examples: Being forced to present evidence to the guilty party so they can take it away. You would think Phoenix would have LEARNED by now.
While AAO is capable of generating random outcomes, for some reason people don't use this much. I don't think anybody's broken this one yet, in the sense of having randomized death or inconvenience, or a statement that only yields new testimony on 50% of presses.12. Not to depend much on luck
Small chance variations add to the fun, but only small ones. The thief in "Zork I" seems to me to be just about right in this respect, and similarly the spinning room in "Zork II". But a ten-ton weight which fell down and killed you at a certain point in half of all games is just annoying.
THAT WASN'T A SUGGESTION, BY THE WAY.
If I'm stumped by a good puzzle and see the answer, my response is "How did I miss that?!"13. To be able to understand a problem once it is solved
This may sound odd, but many problems are solved by accident or trial and error. A guard-post which can be passed only if you are carrying a spear, for instance, ought to have some indication that this is why you're allowed past. (The most extreme example must be the notorious Bank of Zork.)
If I'm stumped by a bad puzzle and see the answer, my response is, "How was I supposed to see that?!"
If I get past a bad puzzle and the game makes it unclear how, my response is, "Huh, did I just hit a bug, or did I really solve it?"
The second two scenarios are to be avoided. I think people still have arguments about the physics of the solution of 2-3, for example, or the mechanics of where the fingerprints were in 2-2, or what the hell ANYBODY was thinking in 3-5.
In adventure games, red herrings are often totally useless items. AA casewriters are laudably reluctant to clutter the CR with trash, but don't necessarily have the same attitude towards red herrings in dialogue. If someone acts insanely suspicious, there should be a reason for it that the player can work out. People should not act like murderers just to be sporting to the real murderer and give them a chance to pass unnoticed; most people in this kind of situation will try not to look like criminals.14. Not to be given too many red herrings
A few red herrings make a game more interesting. A very nice feature of "Zork I", "II" and "III" is that they each contain red herrings explained in the others (in one case, explained in "Sorcerer"). But difficult puzzles tend to be solved last, and the main technique players use is to look at their maps and see what's left that they don't understand. This is frustrated when there are many insoluble puzzles and useless objects. So you can expect players to lose interest if you aren't careful. My personal view is that red herrings ought to have some clue provided (even only much later): for instance, if there is a useless coconut near the beginning, then perhaps much later an absent-minded botanist could be found who wandered about dropping them. The coconut should at least have some rationale.
The very worst game I've played for red herrings is "Sorcerer", which by my reckoning has 10.
If a certain solution is banned, please give me a reason that makes sense in the context of the story. If I'm not allowed to go somewhere or present some piece of evidence, please tell me why. 1-5 does this very well when it comes to a few compromising pieces of evidence, having special dialogue in place to catch these presents.15. To have a good reason why something is impossible
Unless it's also funny, a very contrived reason why something is impossible just irritates. (The reason one can't walk on the grass in "Trinity" is only just funny enough, I think.)
A case should never hinge on some culturally local fact, still less so on having played all of the canon games or your own favorite crossover series.16. Not to need to be American to understand hints
The diamond maze in "Zork II" being a case in point. Similarly, it's polite to allow the player to type English or American spellings or idiom. For instance "Trinity" endears itself to English players in that the soccer ball can be called "football" - soccer is a word almost never used in England.
PACING!17. To know how the game is getting on
In other words, when the end is approaching, or how the plot is developing. Once upon a time, score was the only measure of this, but hopefully not any more.
If the player doesn't feel that progress is being made and the plot is going forward, it is simply unfair to expect them to keep playing until it heats up.
Giant surprise super-long endings will not necessarily endear you to players. One fake ending is kind of pushing it (it's overdone). Two is really pushing it. Three or more, and you will see complaints. (SEE: AAI).
Addenda:
The player has the right...
Not to be required to remember tedious minutiae that are not listed in the Court Record.
Major facts of the case, yes. Minor details? That may be a staple of mystery novels, but computer games aren't mystery novels; the player has no ability, short of restoring an earlier bookmark, to actually "flip back the pages" and check. And rechecking text in a AA game necessitates a great deal more tedium than is involved when reading a book, due to all the roadblocks to fast reading.
A puzzle that hinges on a minor remembered detail also effectively renders the game unwinnable to anyone who has happened to forget it... practically speaking, unless they're honestly expected to present every profile and piece of evidence to every statement. Our time on earth is limited, and there are so many better things to do with one's life than jump through hoops for an author.
Not to be required to answer a question incorrectly in order to proceed.
Even if the player-character is fooled, the player might not be. Asking the player to present something that they know is wrong is to ask them to get the wrong answer that you ask for, but not any other wrong answers. How is the player supposed to distinguish the false theory you so elegantly planted from all the other false theories they could propose? Better just to ask them to say CORRECT things.
Not to be required to sit through a premature Guilty verdict, which is quickly reversed, in order to proceed.
It was interesting in the first AA game. It's just plain tiresome now.
Not to be required to solve problems in an arbitrary order.
If the player sees the answer to the crime early on, this should not make the trial MORE difficult by muddling what they need to present. Requests for presentation should be clear enough in context that having extra information doesn't ruin them. Otherwise, you ask the player to be smart, but not too smart, and penalize them for being clever.
Not to be subjected to excessive in-jokery.
A few AAO in-jokes in descriptions is fine. But in a few years, when the people you talk about aren't seen around here anymore, how well is the case going to play?
A bonus of removing excessive in-jokes is that they are almost never funny, even to the people who are in on them. They are usually only funny to the teller.
One in-joke per trial segment, maximum, is about right, I think.
Not to be subjected to memes.
By the time most people play your trial, the meme will be stale. Their annoyance level will be high - quite high, in fact, if you were to measure it on some kind of numerical scale.
Not to have to spend too long dealing with truly obnoxious characters.
The canonically obnoxious characters have some limits to their awfulness. AAO fancases just don't know when to stop. Oldbag will go on for TEN pages of dialogue, rather than three. Even moments that should be satisfying, such as a breakdown, get turned obnoxious by this effect of exaggeration.
The joke should not be on your player.
To fight their own battles.
The player should be able to have some sense that they actually solved some kind of problem or dealt with some kind of tough situation. If the aide or the Prosecution does everything, or even if the player-character solves the problem without the player's direct input, they will not be satisfied.
This was demonstrated quite well in Apollo Justice.
To not have to fight absurd battles.
On the other hand, arbitrary obstacles, such as a witness who lies six times and faces no consequences at any step of the way - or a Prosecutor who does the same - are obnoxious. The bad treatment shown to Phoenix is pretty much the limit, I think - anything worse is pushing it.
Not to be subjected to deliberately false or misleading co-council/inner monologue hints, unless the co-council is the culprit.
One bad case for this is that confrontation in AAI, in which Edgeworth implies that a totally different contradiction is called for than the relatively simple one at hand. I've seen "lying inner monologue" pop up in fancases, too.
Giving someone a false hint ("I NEED TO FOCUS ON THE DOOR TO THE ROOM" when the contradiction is the color of the victim's tie) is like throwing someone a life-preserver made of lead. It breaks trust in the author.
To have the Prosecution's current argument and the purpose of each testimony be clearly articulated.
It is one thing to ask the player to tease out a contradiction from testimony. It is quite another to ask them to rebut a vague argument that could be interpreted in many different ways! If testimonies appear irrelevant or speculative, and the prosecution seems to be throwing around vague, unsubstantiated accusations, how is the player expected to follow - or care?
Figuring out what the witness is saying should not generally be the puzzle. (If it is, then great care is required). Likewise, figuring out that the Prosecution's vague, dubious argument has one hole in particular the author cares about is not a good puzzle.