Borderlands 2 - free with new video card. Had fun with this but overall I felt it was wanting in some important areas, in particular I think they may have shot themselves in the foot with the overly complicated stat systems and limited inventory and ammo space. Spending as much time trying to work if some random crap is an upgrade takes way too much time out of shooting stuff in the face. I also felt the skill systems were lackluster, too many weak passives with no significant effect on gameplay. Also, part of it is me sucking, but I felt the difficulty has a little too high to be fun if you started getting bad luck in drops.
Diablo 3 - paid more for this than every other game this year combined. Not worth it. Probably not worth it even if it was free.
Defender's Quest - interesting mix of tower defense and jrpg style, where towers are characters that you recruit and gear/level up.
Endless Space - a fair attempt at capturing some of the fun of MOO2/SE4, let down by a pretty terrible combat system
FTL - brutally unfair and wildly random, this one was entertaining in the way most roguelikes are, with the bonus of the fairly unique star trek'esque setting
Guild Wars 2 - Solo PVE was entertaining, group PVE sucked huge donkey balls, not interested in team pvp. Overall worth the money for what I got out of it, I was hoping for more though.
King's Bounty: Warriors of the North - more king's bounty. Nothing innovative here, if you liked the previous ones, you'd like this one, if you were bored with previous ones, avoid.
Legend of Grimrock - nice flashback to eye of the beholder
Magic 2013 - never played any of the previous ones, this one provided a lot of entertainment unlocking everything, but after that it seems to be pretty much multiplayer or go home
Mark of the Ninja - not played yet
Orcs Must Die 2 - Worthy sequel to OMD, with the word of warning that *everything* is built for co-op and it can be frustrating single player. ( You have two or more simultanenous waves of orcs from different directions with inadequate trap support from map 2 and almost every map after, expect a lot of running back and forth and killing stuff by hand if solo )
Torchlight II - a lot better than Diablo 3, but didn't hold my interest for all that long regardless, I think I am just tired to the format ( PoE did nothing for me )
Tropico 4 - not played yet
Witcher 2 - not played yet
X-Com: EU - great fun, a little less depth than I would have liked, but I thoroughly enjoyed this one.
Ironically the game I had the most fun with this year I bought during a steam sale last year - that was Saints Row 3.