I liked both. After scanning the reviews (especially user reviews), I was worried DA2 was going to be horrible. My fears were completely unfounded.
DAO was more epic in scale, but superficial in the sense that you'd resolve some conflict (gaining an ally) and then move on to the next bickering bunch, completely forgetting the first ally. DA2 seemed to revisit local situations/people multiple times, and the decisions you made earlier had at least some effect on the next encounter. If nothing else, I appreciated the variety.
Combat didn't seem overly different to me, but I play as a straightforward archer on Casual, so that might explain it. Companion AI still sucks at taking potions, requiring heavy babysitting when things get hairy.
DA2's heavily recycled maps are the main sore point. We're already revisiting the same location multiple times, there's no excuse to recycle dungeons in different locations.
Characters - hard to pick. I really liked Allistair, Leliania, and Anders from DAO/DAA. I really liked Varric and... eh, the rest were ok. Aveline had some good moments. I liked that DA2 gave you chances (especially at the end) to get your companion's input on a situation. I liked the inter-companion dialogue when you walk into a companion's house, and that them having a place of their own lets you see them differently than DAO's just-waiting-around-in-camp. However Shale >>> Sebastian, though Sebastian seemed better connected to the main plot, what with him being in the Chantry and all.
Loved the narrative framing device (Varric's interrogation). Replaying the prologue makes me appreciate it more now that I've finished the game.
On to the DLC....