Chiming in as another member of the "Actually Really Liked DA2" Squad.
Well, before I say anything, I've gotta admit that DA2 had some serious, serious issues. I could stomach the repeated environments the first time through, but they became unbearable on subsequent playthroughs. And yeah, the plot completely goes to hell in Act III, though there's still some interesting stuff going on there.
However, the main reason I stick up for DA2 is that it's the first Bioware game in forever that wasn't structured exactly like every other Bioware game. Quick, name this game: you start off in a fairly peaceful setting, but stumble upon a bad guy's plan, and in the course of getting involved discover/gain some unique power that only you have. Then you travel around, meeting new companions and seeing new sights and doing tons of sidequests, until, about halfway through the game, there's a sudden dramatic twist/revelation that casts a new light on everything you've done since the beginning. Then you do some more stuff, eventually returning to the major city you've been operating out of to confront the villain in the heart of your civilization's power.
If you answered Baldur's Gate, Knights of the Old Republic, Jade Empire, Mass Effect, or Dragon Age: Origins, you are correct.
DA2 broke that mold by basing the plot around a single location over the course of several years, telling the story of Hawke and Co. as they matured and built lives for themselves. Instead of being a straightforward adventure, it was more about how a series of events shaped these peoples' lives, and the city of Kirkwall. It was really more like something Obsidian would have come up with, and I'm one of those suckers who's willing to overlook the major flaw that every Obsidian game has because the writing's always fantastic.
Now, again, everything kind of fell apart in the third act, but at least we'll always have the awesome look into Qunari culture and philosophy from Act II.
Also, I thought that each of the party members--well, except for Isabella and Sephirelf--were pretty interesting and well-written. Varric was just great: always useful to have around and usually a fun addition to conversations. Ditto Aveline. Merril was unique: an obvious "cute geek girl" nerd-bait character a la Tali, but one who was so blindingly naive that you couldn't help but hate her. And then there's Anders, who, while he might have been a creepy, mentally unbalanced idiot, was at least interesting. (Plus, if you brought him along with Varric and Isabella anywhere, it was basically a nonstop snark-fest.)
Plus, a bit of fridge brilliance: I thought it was stupid and ridiculous how many enemies would come pouring in to fight every time you got into a skirmish, too. And then I realized that the whole game was framed by Varric retelling the story to the inquisitor; he was just embellishing the insane amounts of violence to punch it up a bit.
Echoing everyone else above, I think if EA had actually given the devs enough time and money to make a proper sequel, the general consensus on the game would be very different. As it is, it's a game with a lot of interesting ideas, most of which never really got to be fleshed out.
And now that the "A" team is back from making The Old Republic, we can expect DA3 to fall right back into the usual Bioware formula. Yay.