If you haven't seen it, there is a very interesting interview with Monte Cook on The Id DM where Monte Cook talks about what he things a good game design should -- and should not -- do. Read it here: Ego Check: Monte Cook, Game Designer & Author. While I respect Monte Cook more than I do many current professional tabletop RPG designers, I strongly disagree with most of what he says about RPG design in this interview.
I was going to write a long counterpoint to the game design positions he takes in this interview when I discovered John Morrow had said just about everything I wanted to say (and probably said it better than I could have in this post on theRPGsite.
You will want to read the Monte Cook Interview first, then read John Morrow's post as the latter will not make much sense if you have not read the former.