I guess for me it's the GTA series and sportsims like Madden and NBA Live.
I can understand the appeal of the GTA series and I have tried giving each one a chance., it's just that after several hours of playing it begins to bore the shit out of me. I think it has to do with the look and feel of the game. The look of the world always came off as bland to me and the controls never quite felt right. It was like they were cramming all these games into one, but none of them played better than the ones I've already played. I do like the radio stations though. Those can be pretty funny.
It's the same thing with sportsims too. I guess for me it was always more fun to watch a sport and actually play a sport than playing the game form of the sport. I guess I just prefer the more arcadey version of them like NBA Jam and Hot Shots.