I think that the biggest reason people are disappointed is that the overall story feels disjointed and a little anticlimactic. It's not the story of Hawke going on an epic quest to save the world. It's the story of Kirkwall, not of Hawke. He's not Shepard - at the end of the day his job isn't to kill the Reapers or the Collectors, and he's not the Warden, where his job is to destroy the Blight. He's just a dude. A champion of the people, but not a world-saver.
I find that interesting and I find the individual character interactions to be amazing. I can see why some people wouldn't, though.