I've been trying to think through this in my head
CoD 4, 50+ hours
FIFA 12 or 13, I lose count, but a serious serious amount of time
GTA IV, 60-70 hours
GTA V 50 hours
Uncharted 2 maybe 70 hours, about 5 or 6 playthroughs with some online multiplayer thrown in
Kingdom Hearts I.5 HD Remix, I think I spent like 80 hours through my 3 playthroughs if I add it all up, worth it for the platinum
Ni No Kuni probably wins for now with it's 80 hours
Technically, FF X wins since I spent 130 hours playing it via BC, but give it a month or 2 and FF X HD will be the winner. I'm like 15 hours through now {that includes Vita playtime though}
* Persona 4 Golden is currently sitting on about 110 hours on Vita
EDIT: Skyrim with 60 hours and there are probably some others that I have forgotten...
