For me, it's got to be Diablo III.
I was a D3 "hater" for awhile (not really, but a bit). Basically, I saw the cartoon-ish, colorful graphics style and being a big Diablo fan (and to an extent Diablo 2), I thought it didn't look right for a Diablo game. Well, by chance my old man and I started playing it in local co-op on the Xbox 360, and whoa. The game is crazy. It's certainly a Diablo game, even though at times you feel like you're playing Baldur's Gate: Dark Alliance on steroids. But, there's lots of loot, more story than usual and all the usual Diablo-style things you'd expect, except they ratchet it up to the maximum degree and polish it to an even higher degree.
The thing that surprised me most was the combat and character development. Holy hell, combat is incredibly satisfying and equal part cerebral, strategic and fast action. You have to develop your character well with the synergies and attributes you want, but you also have to execute under pressure and manage your character in combat well. It almost has the feel of a twin-stick shooter at times, which is really odd, and ramps up the speed and frantic action, but somehow it just works *really* well. I think it's my favorite 3rd-person action combat ever.
Other things of note is how much they squeezed out of the X360. My god, I have no idea how they got this thing running as smoothly as they did with all the particle effects, etc. It's buttery smooth and again polished extremely well. There are downsides, such as the console UI being bad in some ways (what do you expect, I guess), but overall it's really impressive that they got it working as well as they did on the 360. I mean, the game looks really nice to boot (it has nothing on the PC version, obviously, but it's very impressive for the console).
I'd say if there are any D3 haters like I was reading this, stop what you're doing and check it out. At least if you're a previous fan of D1 or D2, it's definitely worth checking out. Or, if you want a looting/character development dream with the combination of fast-paced yet thoughtful combat, you should play it ASAP. Big surprise for me.