It's probably more useful to do rules of basic CRPG design, but maybe later, because these are what's irking me now.
Rule 1: The first two hours of your game should be infinitely replayable. This means I should be able to skip your cut scenes. Seriously, are you retarded?
It also means that the first two hours of your game should be mostly NOT running around someplace talking to people. That's fine and dandy the first time, but upon replay it's shitty.
Rule 2: Your ending should leave a fuzzy feeling. The best ways to do this are to 1) actually resolve plot threads and 2) give the player a lot of information about what happens to the characters/places in the future (a playable post-level is best).
Endings which don't resolve the plot's errant threads and don't actually let you know what lies in store are pretty shitty, especially for an RPG.
Rule 3: Don't punish players for not reading your mind. Too many RPGs let you choose your upgrade path, only to later reveal that the path you chose is really bad, at least for you. This is a very serious issue that is mostly a problem for the games that let you upgrade each level. Because you cannot take back a level and because each level is more difficult than the previous one to achieve, a mis-step will make your character suck. Especially in games that scale your encounters to your level.
This is not a problem in games that let you work to gain skill points. For example, instead of giving you a skill point per level, a new level simply unlocks the next tier of a skill. Actually buying the skills is done with some kind of skill mark that you get for killing shit or something. These are not strictly limited, they're just expensive to obtain in terms of time. You have to use N skill marks to increase your skill from N to N+1.
Now if a player mis-steps, it's not crippling, it's just going to cost him time.
I guess that might be a basic design rule, actually...