As I've said I'm on the point I'll just have to vote whatever I've played and for this year it's... Criminal Girls.
OK, now hear me out.
The game does have one of the best battle systems ever in a turn-based RPG (and I've played some). Every turn it randomizes one of the attacks available to each of your up to 4 characters and player decides which characters action to use. Aside simple attacks (or healing) by that character, the learned options include attack by 2-4 characters and attack of that character with certain other one. In half of such games battle is 95% of time choosing "attack" and even in games that do magic right the currently best magic just replaces attack for some characters. This was a really interesting system and that - ahem, among other things... - makes it an enjoyable game.

Holy shit, I want to amend my earlier commentary now because I didn't realize that Cart Life came out in 2010! That's probably because I didn't discover it until years later after it came out on Steam myself. But with that knowledge in tow, let me now say that Cart Life is my favorite 2010 game! It's an indie poverty simulation game where you choose one of a few street vendors to play as (and your choice does make a narrative difference). It's not a "fun" game to play. That's not the point. The point of it is to convey understanding of the kind of experiences, both positive and negative, that lower-income people have. While I've never been a street vendor before, I speak from life-long experience in the lower-income category when I say that I appreciate the honesty with which those experiences are conveyed. Namely I appreciate the game's lack of artificial dramatization; its understanding that these situations are inherently dramatic and don't need to be "spiced up" for entertainment value. Nothing supernatural or science fiction-y here. This is just very believable human beings trying to make it from day to day, maintaining their relationships, attending hearings, all the things. If you've been in a situation of economic struggle before, you'll appreciate the way that this game sees you, and if these experiences are foreign to you then you'll find a path to empathy here.

That said, the version I have has some real technical issues (like unpredictable crashes that occur too often) that don't exactly enhance its unusually earnest attempt at life-likeness. It's still my favorite game from this year anyway. Just didn't want to let that go without mention after I looked up its original release date. Games don't have to be flawless or "fun" to be valuable experiences worth having. For a fuller picture, here's the review that originally brought Cart Life to my attention:

To me, DKCR is probably a 7/10. It doesn't live up to the SNES trilogy. They got like one or two right things, and then A LOT of wrong things.

Also, it's not underrated. It got a lot of praise.

I don't think it got enough praise though personally; for me it's one of the top ten best games on Wii. 

The kinetic pacing of the levels and the way they shift and transform as you move through them is phenomenal.

Not much surprise to this year, because there were two games that were clearly standing out in the poll.  The 2010 Game of the Year is Super Mario Galaxy 2 and the runner up is Xenoblade Chronicles.

Alpha Protocol is the coolest game ever, I replayed it many times.