Bit Tech published an editorial that discusses the limits games designers impose on themselves when they try to make games in certain genres.
"The thing is, I do really wish we could throw off the genre limits and rediscover the freeform game design of the early years of gaming. Sometimes when we try, it falls apart terribly (Trespasser), but often it works wonders. Portal belongs in both the FPS and puzzle categories and is all the better for it. Spore will hopefully create a whole new category, as did The Sims.
When you forget genres and just sit down and think " Let's make a cool game," without any pre-conceptions, then you stand a chance of making something really good. I remember back in my wannabe-rockstar days, I was a big fan of two bass players (Stuart Hamm and Billy Sheehan) who both had very showy and complicated playing styles. Stuart Hamm once said he'd deliberately avoided seeing how the other guy played because if he saw him it would lock him into doing things the same way, and prevent him working out his own style. I think he has a very good point."