This is the text from a post to rec.arts.int-fiction from 1993. It's written by Graham Nelson and talks about the expectations that players should be able to have of text adventures (interaction fiction), but I think some of them are applicable to table-top roleplaying. You can find the original post and responses on Google Groups. It is also on the web as part of a group of articles on the design of adventure games, by the same author: The Craft of Adventure.
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. Mention of which brings us to:
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.
A more sophisticated version of (1) leads us to:
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.
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.
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.)
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.
8. Not to have to type exactly the right verb
For instance, looking inside a box finds nothing, but searching it does. Or consider the following dialogue (amazingly, from "Sorcerer"):
(with the small key)
No spell would help with that!
(with the small key)
The journal springs open.
This is so misleading as to constitute a bug. But it's an easy design fault to fall into. (Similarly, the wording needed to use the brick in Zork II strikes me as quite unfair. Or perhaps I missed something obvious.)
9. To be allowed reasonable synonyms
In the same room in "Sorcerer" is a "woven wall hanging" which can instead be called "tapestry" (though not "curtain"). This is not a luxury, it's an essential.
10. To have a decent parser
This goes without saying. At the very least it should provide for taking and dropping multiple objects.
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.
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.
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.)
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.
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.)
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.
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.