In this order:
1) The Elder Scrolls V: Skyrim
2) Portal 2
3) The Legend of Zelda: Skyward Sword
4) Deus Ex: Human Revolution
5) Super Mario 3D Land
Some runner-ups: Dead Space 2, Battlefield 3, Minecraft, L.A. Noire and Mortal Kombat.
Note I haven't played some of this year's bigger games though, like Arkham City, UC3, Sonic Generations, GOW3, Assassin's Creed, The Old Republic and any others I might be forgetting.
I'm of course not 100% certain. The two games that blew me away the most were Skyrim and Portal 2, and I'm absolutely certain of their positions. Below that though... I dunno. Zelda was terrific, and I loved it, but it was a letdown in some respects, so it's definitely not at the top of the list. 3D Land was also really great, but it's a portable game so it's more of a streamlined experience anyway.