It wasn't really a combat reliant game. I'm somewhat of a supporter of Mass Effect 2; not because of the combat (though I found the combat entertaining), and certainly not for the mining (which I actually didn't mind as much as the rest of the gaming community, I found something meditative about it). No, the real reason I like Mass Effect 2 is something most game makers haven't really delved into yet: Meaning. Theme. The thing that turns media into art, sparks thoughtful conversation, and propels gaming from something we do for shits n giggles into something attune to reading a classic novel (except instead of the bland bits that come with reading a classic novel, you get explosions).
One of my favorite examples of this in ME2 is one you can find on the escapist. Extra Credits did an episode detailing a particular mission
http://www.escapistmagazine.com/videos/view/extra-credits/1974-Enriching-Lives
The mission basically comes down to exterminating a large portion of the Geth still hostile to commander Shephard, or converting them to friendly Geth. Outwardly the choice may seem pretty black and white. However; this mere, fictional decision actually made me change my opinion of religious extremism (more specifically, the Taliban and insurgent groups in the Middle East. Also I respect the opinions of Conservatives and Republicans more). This wasn't the only mission in the game that broke out the difficult questions. That asked what it meant to be the one making these decisions and thus imposing your will upon a huge spectrum of living, breathing, sentient organisms (well virtual ones anyways).
Aside from that, like I said before, the game isn't about combat. Combat's there, but this is a game about the power of words. The first of what I hope are many games that look (at least slightly) away from blood, guts, and guns, and look more at anaphora, parallelism (see what I did there?) and debate.
I'm not saying Mass Effect is perfect, or even that it deserved game of the year; Mass Effect's main problem is that the choices we (the players) do get to make have no real consequences. If you go the Paragon route things will end up happiness and rainbows no matter what. There's no negative recoil for trying to save everyone, and so why would you pick Renegade for any other reason than to be a slightly more evil good guy? Renegade should have some kind of player pay off. Paragon should be an emotionally turbulent route, you should have to pay for the happiness and rainbows. Like when you payed for Ashley's life with Kaiden's (and then regreted breaking bros before hos).
Anyways. I like the Mass Effect series, ME2 in particular. I think it's more than just your average shooter and most of the praise is deserved. Everyone's entitled to their opinion of course, these are just my reasons for mine.