I love the true ambiguity about which decisions are "good" and which are "evil". In DAO, there were many situations that made me pause and think -- can I trust the werewolves, or should I side with the elves? Is Harrowmont really a good king, or did he poison the old king's mind? But after the fact, I always knew who was right and who was wrong.
After finishing DA2, I honestly don't know whose motivations are the "right" ones. I played the entire game trying to be a good, decent person... and by the end I doubted myself and my convictions completely. While my decisions may have been idealistically correct, they didn't always result in predictable outcomes, and I didn't automatically get a happy ending because I had been a "good" person. I love that there are consequences no matter what your choices are, and that you can play a kind, decent character while siding with the Templars or with the Mages. All sides have valid arguments, so there is no straw man villain to despise.
In most games, you can either be a diplomatic saint; or a raving, bloodthirsty psychopath. In DA2, I feel like I can play many different shades of good, making different decisions over multiple play throughs.
I also love how the story itself is told. Varric's cut scenes provide wonderful foreshadowing, and a convenient way to skip forward in time. I love it that you see events unfold over a long period of time, and that the city tensions escalate on a more realistic time table as a result.
There are many other things that I love about DA2, including the refined game-play mechanics, the characters, and the many opportunities to delve deep into the culture, philosophies, and politics of the city. I finally understand what the Qun demands and why Dalish elves are misunderstood by outsiders. I get why mages want to escape the circle, and I also understand why templars think apostates are dangerous.
All this being said, I also love and adore DAO. They are different games, with different strengths. Can't wait for DLC and DA3.