As a foundation, these are the games and the lessons I learned from them:
-Combat will absolutely kill you. Often in stupid ways. Avoid it where you can.
-A game doesn’t, and shouldn’t, have to be entirely focused on combat-related characters.
-A well constructed world will almost generate its own adventures.
-Rule may help control the fun but rules are not the fun themselves.
-If in doubt, make something up. Or have something explode. Or shoot the lock to lock the door. OR shoot the lock to unlock the door.
-No one gets left behind. Everyone gets something to do.
-What characters say they are, and what they really are, are always two different things.
-Rules may not control the fun, but elegant rules can definitely generate some fun of their own.
-Characters will go as deep into a world as you let them, or a lot of the time, as deep as they want to cheerfully barging obstacles out of the way as they go.
More recently, I’ve found myself learning from the design work on games like Gumshoe, Blades in the Dark, Sig and Iron Edda. In each case these emphasize narrative and story over ‘You rolled a 1 therefore I will burn your character in front of you’. The willingness to fold character consequence into game design is very cool and is, as near as I can see, an evolution of the work begun by the other games I talk about here. Or to really drive the joke home, rules CAN help control the fun and truly great rules will also help create fun too.