no need to worry about listing top tens and just one game, just mention the games you played and enjoyed this year, it also doesn't matter if the game is released before this year.

Mass Effect 2. Was my favorite by a lot

I also liked Metro 2033, Fallout New Vegas (am currently liking), starcraft 2.

Dissapointed a lot in. Supreme Commander 2. :( haha Supcom 1 is my favorite RTS ever... :-/ despite it's flaws.

ha i guess you're the only person with a PC

i enjoyed SC2 a lot , mainly because i haven't played an RTS in a long time (i wouldn't count C&C 4 and RTS... it was weird)

StarCraft II. I've been having a blast with the game. Even if it barely runs on my laptop. Also, The Orange Box has been a lot of fun to revisit :)

Call of Pripyat

Starcraft 2 

metro 2033

Dawn of war 2 

alien swarm

Mass Effect 2 and Civilization V, though I'm pissed with Civ V bugs so I'm kinda waiting for 2K to patch the game some more. :/

Starcraft 2 is defiantly up the top, good campaign (story was disappointing tho) excellent multiplayer, can't wait for HotS.

League of Legends was fun for a while even if I sucked at it.

from what I have played of Recettear the game will be hours of quirky Japanese fun.

Shatter was my surprise hit of the year.

started playing X-Com again after all these years the game is still great.

Minecraft.

mmm minecraft 

Minecraft and Metro 2033 are my favourite PC games this year. Still play a lot of Left 4 Dead 2.