For me it would have to be GTA4 or Skyrim. The aesthetics in those games are just amazing. I really feel everytime I play in those worlds that I'm in those worlds. The detail to those games is amazing.
GTA4 had a good story.
Skyrim had dragons.
If I had to pick though.....I guess I would pick....I dunno. I gotta think about this one.
Edit: "this generation" meaning the console cycle but include PC games during this gen as well. I know there isn't a generation or what have you with PC, but since most PC games haven't escaped this console gen I'm starting to lean towards the "generation" thing with PCs.