It was definitely a close race between the two top games here, but in the end StarCraft II: Wings of Liberty edged out our runner-up. StarCraft II shipped with Blizzard's requisite level of polish and tons of content, which was quickly snapped up by a huge community from casual players all the way up to Korean progamers. In fact, some of us played the StarCraft II beta more than most other games this year, which continued when the game was released.
While the RTS genre wasn't dead by any means--we love you Relic--StarCraft II seems to have relit the fire, getting the eyes of a broader audience by going hand-in-hand with eSports, YouTube shoutcasts, and livestreaming.
Runner-up: Civilization V
Sid Meier's Civilization franchise is a PC staple and we love this streamlined version of the game because it fully satisfies that "one more turn" addiction that has been with us throughout the franchises entire life. The move to hexes and abolition of unit stacking do wonders for the combat system, adding some real strategic and tactical choices instead of playing "Whose Stack is Bigger?"
Not trying to be a dick, but just wanted to point out a typo: In the last line of the Runner-up column, "Who's" should be "Whose". My fingers mutiny all the time on words like that. :-\