I haven't played a whole lot this year, so my vote goes to Borderlands: The Pre-Sequel. This game is basically stopping me from playing anything else right now (as did BL1 and BL2).
Yeah, it's a lot shorter than the other 2. DLC seems pretty lackluster. Farming is an issue due to lot of one-time bosses. Nonetheless, the game is fun, has the trademark humor, and fits well within the Borderlands series.
The other games I've played this year were older games. I would like to take a look at Geometry Wars 3 though.