It's hard for me to really choose a "game of the year" because this year has been very disappointing to me overall. Very little in the way of truely epic RPG experiences that haven't been literally ripped apart by their flaws. "Mass Effect 3" was too shooter-ish for my tastes for example, and then that ending pretty much invalidated any praise I might have had for the story.
I suppose if I had to pick one it would be "The Secret World" for all of it's flaws it tried to do something very differant in the MMO scene, it has quite a good world and story behind it, and while the mechanics and customization were not all I hoped for, they are surprisingly workable. This game was however considered to be something of an "epic fail" so I guess I'm on a differant wavelength from most people.
I did put a pretty substantial amount of time into "X-Com: Enemy Unknown" but it got repetitive, and honestly didn't have quite the depth I was hoping for. Had they included more varied maps, more features and tech, and more things you could do with your Soldiers I might feel differant about it. To me it seemed like a decent skeleton for a game, but one where they intended to inevitably expand it through dozens of DLCs.
"Borderlands 2" was okay for a shooter, but honestly I didn't much care for the whole "golden key" system, especially seeing as I don't use twitter. Made me feel like I'm losing out and being punished for not embracing social media and instead primatly just playing the games. I do play to go back and finish it a few times, but playing a couple of MMOs (TSW, STO, and a little GW2 when I have time) all very casually nowadays I haven't put a lot into Borderlands 2.
For me "Diablo 3" was probably the biggest disappointment of the year, to be blunt it struck me as being vastly inferior to years older titles like "Sacred 2" which did more to innovate in this genere than I could have expected. I tried to do "World Of Warcraft" again (forsaking my other MMO interests), hoping my guild would reform for the new expansion (which didn't happen) as much as I disliked the "Panda" idea. The big turn off for me was that WoW decided to simplify itself even further, taking everything I hated about Diablo 3 and pretty much putting it into WoW as mechanics. No more talents or anything... yuck.