Since I havn''t played all the games released this gen I really can't say for sure. There is a few games I do't have yet that could possibly be here (*cough* Skyrim) and I won't count PC exclusives as I'm not much of a PC gamer (sorry STALKER, as much as I love you)
And this list could easily change the more I think about it so I'll just knock it out without thinking too much about it.
Fallout 3
inFamous 2 (or perhaps the first infamous, it had a better story and characters and more varied factions, but less interesting city less powers, sort of a toss up between the 2)
Red Dead Redemption
EDIT:
HigherTomorrow said:
Forgot this until I saw quoted post. How could I forget one of the greatest gaming experiences of this generation. I also thought MGS: Peace Walker was just as fun but quite different and not easy to compare.
I know that's technically 6 games altogether but I'll stick with my original 3 just to avoid thinking about it too hard.