For me it boils down to a handful of things.
A: The combat is not changed enough. Sure it's better, but not much. Tapping the attack button didn't really do much for me, I don't FEEL like it really added anything. The combat still feels distant. I enjoy the story and the characters and kinda want to fiddle around with them more, but the combat just puts me to sleep. It's not fun, there are always too many enemies that just gang up on you, surround you, attack your healer and there is very little you can do about it. There are no tactics, no traps you can set, it just feels random chaotic and boring. The sad part is even with fights being such slogs, they are still too easy. It honestly takes a great deal of fun out of the game for me. Also the way they limit stamina Regen for warriors seems like a needless kick in the nuts. In fact nobody seems to have good regen at all for prolonged conflicts. That might be the point, but it seems a bit hollow when it ends up meaning everyone just starts sucking down potions. It's less about having good tactics and more about just paying attention.
I don't mind the dungeons, I like the story, but I don't really like most of the characters.
To be fair I didn't like the characters in dragon age origins either tho, so I can't really put it up as a serious mark against it. What I can is the Armor, weapons and the lack of customization. Dragon age origins allowed you to use weapons and armor that were not designed for your "Class" and that was fun. Taking that away pisses me off, and kills some of the characters I want to make. This game works really hard to shoehorn you into your armor and weapons, and makes it impossible to be a viable character while using weapons and armor outside of what it thinks you should. This just sucks. I can live with not changing my companions armor ever, but they should at least give us options, OR just do away with it, and use a mass effect style upgrade system, but either give us customization to freely change out armor pieces, or don't. I know you can use them if you try hard enough but the point is your character isn't going to be any good, as where in the previous game they could still be viable even if you did something odd.
The skill sets are Rigid and a lot of the upgrades don't feel like upgrades and you end up putting points into them just so you can get something else. This is not a good design, and needing upgrades to fully utilize your cross class combos is a terrible idea. All your upgrades should work for you, instead of increasing the damage caused by a cross class combo. Also some trees could stand to use a better description, I honestly don't know what some of them are trying to do, and then when I look at the tree and then at the description they don't always match up in my head. This is something that could easily be fixed, but wasn't. This is lazy design.
I did enjoy DA2 a bunch, but it's been nearly impossible for me to stay focused for multiple plays. The upgrade system just has no flex to it, and very little customization between general play styles. The combat just didn't do enough. I am very disappointed with DA2, but will admit I did enjoy it when it was completely fresh for me. It's just these flaws really hinder me from continuing to play after I've beaten it once, and will keep me from giving a crap about any DLC that might come out for it.