It takes steps forwards and backwards. Story-wise, it's more of a stand-still. It's more interesting (to me, at least) because it is much less standard than Origins' plot. But it makes some serious missteps (towards the middle and end) and gives you next-to-no choice in determining its outcome.
The core gameplay is improved. The combat is much more fluid and interesting, and non-mages are given more options on how they want to build their character. I say "non-mages" because Rogues and Warriors are given a good bit more variety, but mages are about the same if not worse off. The game is easier, however. Basically, whatever difficulty you played in Origins, go one higher in Dragon Age II. I'll probably go up to Nightmare difficulty for my Warrior playthrough, as I'll have more health than my archer and my mage (some enemies have some attacks that can virtually instakill characters with lower consitutions).
Aside from that, I'm a huge fan of the voiced player character. At the risk of echoing Mass Effect's FemShep fans, I think Jo Wyatt did a great job as the female version of Hawke. Meanwhile, the visuals have pluses and minuses. At first glance, Dragon Age II is a much more interesting looking game than Origins. But you'll get familiar with the game's locations...and then you'll get really familiar. Then you'll likely be bored with the looks of the game (and, in the case of inexplicable and blatant environment reuses, you'll be downright annoyed).
Overall, it's one of my favorite games of the year (Probably coming in after Portal 2 and just ahead of Alice: Madness Returns. It is likely about to be knocked down many notches in the coming months though). The flaws are undeniable, but how much those flaws hurt the experience varies greatly from person to person. I was able to overlook them because I enjoyed the core of the game.