Everything I’ve read over the years has expressed a wide variety of goals in game design. Here are the tidbits that have stuck with me:
Simple, but not stupid
Rules should aid in play, not obfuscate it.
Interplay and Counterplay
Both of these concepts are more thoroughly advanced and studied in video games, but I feel that just makes the need for their study and application to table top RPGs that much more important. Interplay is the interactive choices allied players make to reach a common goal. Counterplay is the inclusion of interesting choices when dealing with an opponent. A save or die spell in D&D isn’t counterplay, it is an enemy action resolved by a random number generator. In fact, it’s pretty hard to come up with counterplay examples in most table top RPGs, and is far more rare than interplay.
Clear rules are hard to write but so rewarding for the players of a given game. Numenera is likely the most clear table top rpg ever written, without being the least sophisticated.
I’m sure there are more design goals I’m forgetting and reserve the right to edit this as epiphanies hit me.