I totally agree that Dragon Age II is underrated but it also lacks polish among other problems.
In the case of Dragon Age: Origins and its expansion Awakening, BioWare had years to develop those. In that time they crafted a deep, rich world with its own fleshed out history and mythology, created well-develloped, deep characters (especially the companions), and had all the time they needed to create unique locations that never reused the same floorplan. The graphics were nothing to write home about, but that's never been the focus of BioWare. It's always been about story, characters, and immersion.
Dragon Age II has a good plot, arguably better than Dragon Age: Origins' generic "dark forces have invaded the land and the hero must defeat the dark overlord in order to stop their advance" (something BioWare still did artfully because they're good at playing with conventions, cliches and tropes; something a company like Bethesda mostly fails at due in part to the fact that they don't have writers of the same skill). Dragon Age II was the story of the rise of a man or woman from the status of refugee to Champion of a city-state in the course of a few short years, all the while getting involved in the mounting tension between Mages and the Chantry as well as the disturbing presence of fearsome religious fanatics called the Qun. DA II was all about politics, power, and prejudice. I wish BioWare had been given more time to work on the game because I strongly suspect we would have gotten a game that would have pleased more people.
But maybe beyond the limitations of time imposed on BioWare by EA, some fans were just upset because it wasn't about another Grey Warden (or their Grey Warden or Wardens from the first game; I know I would have liked the chance to import and play mine again) and it wasn't about another Blight and the big bad wasn't another Archdemon. People can be notoriously bad for needing sequels to be more of the same as the previous (be it game, book, movie). Take them outside of their comfort zone and they b**ch and moan about it.
Moving beyond plot, I can't say I liked or understood certain aesthetic changes: the Qunari were fine without horns and elves looked much better in Origins, looking like short humans with pointy ears. There was no reason to make them look like rodents. The pointy ears are enough to help us tell them apart and it's funny that Felicia Day's character Tallis ends up looking like an elf from the first game while most of the others (Merrill being another exception; even Fenris looked like a ferret in my opinion) don't. Kind of jarring. Also didn't care much for the Hurlock redesign.
I liked Dragon Age II well enough, but I agree with some of my fellow fans that it's a flawed masterpiece. I don't feel that it ruined the franchise or anything. I hope BioWare learns from this one because I sure as Hell don't expect EA to have learned anything at all. I hope Dragon Age 3 blows us away!
P.S. Does anyone else feel like BioWare signing on with EA was a deal with the Devil?