Let me start off with a disclaimer: I have not played Dragon Age 1. That said, I do think a good game should be able to stand solidly on its own two legs, at least for the most part; it's just unfortunate that Dragon Age 2 stumbles around the entire time.
Dialogue, as in most Bioware games, shines like a brilliant jewel through the muck. Excellent voice work, and well-thought out conversations are a pleasure to listen to. The banter between party members while you traverse an area are particularly insightful and amusing. Often, if I hear someone start up something with another party member, I will stop running or avoid reaching my checkpoint just so I can hear what their chat will be. Isabela, Anders, and Varric are particularly fun to have in a party for this reason.
It's also yet another advancement that even more people than usual in a Bioware game can be romanced, and that many of them can swing either way to suit your interests and character gender/orientation. Depending on your Friendship/Rivalry with them, that also colors their relationship with you, which is an interesting twist, even though it isn't fleshed out as much as it would sound.
The animation is yet another step in the right direction for Bioware. Facial animation looks much less cut-and-paste than previous games and looks like it's based on what they're actually saying. In general, there's a much wider variety of body animations for conversations as well, which is a welcome change, particularly after finishing a new playthrough of the Mass Effect games and viewing only a handful there.
Hawke, while not as satisfyingly intimidating as Commander Shepard, has been given a little more leeway in how she/he handles situations. I do enjoy the ability to be more of a wiseass when I want, or be threatening without out and out killing the person. The demanding money choice is the only part that seems a little less desirable to bother with, but the fact that it's there as an additional option is welcome.
Combat (minus some quirks, like sometimes being difficult to target enemies and the janky camera when pushed up against a corner) feels fast and furious, even when pausing to constantly enter in specific tactics. The character ability customization/specialization is a nice touch, reminiscent to me of the Sphere grid from FFX. It allows you some pretty good control over what you want your party members to excel at.
Ah decisions, decisions...
As nice as it is that there is a Friendship/Rivalry system (reminds me of Light/Dark side alignments, but without the altered point of view), it's pretty frustrating that the points aren't given out consistently. Sometimes no points are awarded at all when in a situation or making a decision that I felt the character should have responded one way other the other to. It also makes forming a party with your favorites rather difficult because they will most likely be opposed to each other, like Anders and Fenris, who I enjoy in a party but dread engaging in cutscenes with. The nasty side effect to this is purposely going to a spot to change your party members and then entering a cutscene, which requires a lot of constant saving and reloading.
Ugh, get a room already you two...
This Friendship/Rivalry element leads into another disappointment. The party members you come across are amazingly stubborn in their views and beliefs. Despite becoming more trusted by them as you advance in the game, they stick a little too strongly to their extreme-sided beliefs. In Mass Effect for example, I appreciated the fact that you could persuade Kaiden that either aliens weren't all that bad, or that he was justified in being a total xenophobe. Likewise here, it would've been very satisfying to be able to convince some of the characters that they didn't have to be completely gung-ho in siding with either mages or templars. Instead, everyone holds too tight to whatever polarized view they have when you first meet them, and never develop their character in that regard. It just doesn't make much sense that people with such drastically different opinions would so easily party with each other and protect one another.
(As a side note, your brother character is a gigantic arrogant annoying ass half the time... I'm assuming the sister character is the same.)
The extreme sides brings me to another element of the game I dislike, namely how both the templars and the mages both SUCK. I find it incredibly annoying that I am forced to side with one of these groups when I don't feel particularly sympathetic to either. Every time I think that one of them isn't so bad, I end up doing a quest where a templar or a mage goes psycho and people are casualties. It's very hard for me to care about anyone when everyone is so hypocritical and extremist. It makes my Hawke look very wishy-washy when I have to purposely step around issues and support mages in one quest and then turn around and support templars in another. Like the party members in this game, everyone and everything in DA2 is always stuck on the sidelines; very few characters bother traipsing around the middle.
That's good Anders, just use your "it was the Justice spirit, not me!" excuse a little more...
Quests are also handled strangely. Often when I go on one quest, I invariably pick up some random item that ends up completing a quest in town that I didn't even realize existed. It's also not always obvious which quests are going to end up remotely linked to the main plot or just be side ones that go nowhere. The story overall is nowhere near as epic as the previous one, and tries to make it look like they did that because it's trying to be more of an intimate experience, but it's so small that I'm not really sure if the majority (minus a couple obvious parts) of it would have any impact on the Dragon Age world at all.
Kirkwall feels very disjointed as a map structure, and the fact that you can teleport to particular sections ruins any feeling of being part of a large connected world to me. Add to that the fact that each section isn't particularly large, especially compared to map sizes in Knights of the Old Republic and the Mass Effect titles, and you get a definite sense that they skimped on the content. Even worse is something I'll mention in The Ugly...
Just points on a rather sparse map...
It's been a very long time since I've seen a game with maps this badly recycled. It's so egregious that many places use THE SAME MAP for their quests, but simply close off access to areas that aren't used in that quest. One stone door will open for one quest, and then never open in a separate quest with the same map. It's so bad that I'm not even sure they have more than 10 re-used maps at the most in the whole game.
Also, someone at Bioware thought it would be clever to constantly spawn more enemies behind you during a battle FROM THIN AIR. Nothing is more annoying than fighting an established group of enemies in one area, only to find that 3 more had magically popped in behind you and started wailing on your mages. Not to mention it looks pretty shoddy visually to just respawn more on top of existing ones. Have them at least look like they came from somewhere, not just dropped in by some cheap AI.
If this wasn't a Bioware game, I don't know if I'd be quite so harsh (most likely I still would be), but they've established themselves as a solid story-based RPG studio, and Dragon Age 2 just feels like they dropped the ball. Meh story, aggravating polarized characters, lazy dungeon/map creation; it's entirely possible that its development cycle was significantly shorter than their other games, but that can't really be an excuse; if your game needs work, then WORK on it and don't release it yet. Easy to say, I know, but at a certain point studios need to man up and stop letting publishers push them around and force things out before they're ready. We all remember what happened with Knights of the Old Republic 2...