Alphabetically then: Arkham Asylum, Bulletstorm, Crysis, Dishonored, Fry Cry: Blood Dragon, The Last of Us, Saints Row the Third, Vanquish, and Wolfenstein: the New Order. Loved them all for different reasons.
I don't have one. I have been gaming way too long and have played way too many amazing games to be able to pick a single game above all others. I could name some games that I rank at the very top of the heap, but thats about it. Just off the top of my head, I would say games like Mass Effect 2, Diablo 2, Skyrim, Day of the Tentacle, Secret of Monkey Island, Knights of the Old Republic, Fallout 3, Half Life 2, Warcraft 2, Dragon Age Origins, etc. Again, just way too many games, in way too many genre's to be able to narrow it down to a single game. Just not possible for me.