GTA peaked for me on the PS2. Now, so many games incorporate it's open world structure and mechanics that it's just another game series.
I've never been able to truly get into it because my moral compass steers me the other way. After watching so many of my friends go around beating down hookers, doing random drive by's and pulling off other twisted acts of debauchery, and then hearing them talk about it so casually, I realized that playing GTA would make me feel like a monster.
I'm not going to pretend like I'm holier than anyone else; I play plenty of games that involve killing enemies, sometimes in brutal and sadistic ways (Madworld, No More Heroes), but those games are lot more stylized, a lot less focused on creating a realistic atmosphere, and everyone you kill in those games is a combatant bent on killing you. I can't go around shooting and stabbing random civilians off the street.