Buggy but worht playing!
You can keep playing with the character you created for Dragon Age Origin. That's what I did but funnily my armor didn't follow with my character so I started the game naked which seemed really odd to me and no armor dropped for me the entire opening. The game was really buggy for me (more than Origin was). It froze a few times, and as mention I start naked, there was some occasional lag too. I'm playing on PS3 but from what I read from forum is that it was buggy for all platform, though it was worst before the patch.
You will see some of your old friend but not many. Most people you'll play with will be new characters. The story doesn't take place in the same location than Origin. You, play in Amarantine and in the Grey Warden Tour and a few new location we didn't really heard of in the first game.
The story is good enough and kept my attention. But once you kill the last boss there isn't much of a ending (not video at least) so don't expect any speech at the end like the previous game. Mostly it's text fact at the end.
Over it's a good expansion and I enjoy replaying it. It's short, more or less 10hours. So overall it worth buying but the game was rush out and is buggy. Save frequently because if the game crash and you didn't save in a long time it might bug you.