It's because so much of it is static design. When you have very non-open areas like this, you can make things look great with nothing more than good static lighting and placement. It's a completely different beast than large, open-area games where the time of day/lighting changes. DAII has the same weather and lighting in every place, except there are night/day version for each area. You'll notice that any lighting that is actually on a dynamic object is very boring and doesn't look very good. Basically, static atmosphere created by good art design makes for good graphics without lots of power needed.
If anyone is curious what it looks like, I've uploaded 127 screenshots so far. They're... massive, so if you have slow internet, I'm sorry. All uncompressed .png at 1920x1080. They're all at "max settings", though the AA still looks pretty bad. Could use some SSAA. I also turned off DDOF about halfway through, because I thought it looked better without it. I didn't really filter them before I uploaded them, so some may be boring, or strange, or very similar to each other. Shouldn't be any real "spoilers". Very few of them show any dialogue.
http://profile.imageshack.us/user/bigassscreens
Just go to the tags on the right and click DragonAge2. I'm slowly uploading the rest I took, but it's slow.
As for things unrelated to graphics, literally all I did today was play this game. The plot is basically broken up into segments with you doing as many side quests as you want before taking on a quest that moves the plot along, followed by returning to the city with time having passed, and basically repeating that. I was worried as I was completing the second "segment" that is was going to be the end of the game, since that was the first time when the plot felt like it had really begun. Luckily, there seems to be a third plot segment, so it's not as bad as I was expecting. I've put an inexcusably large number of hours into this game in a single day though, and I don't really know why. It wasn't THAT good, but I enjoyed it, and I really had nothing else to do today. Good thing it came out in the wake of 3 exams I guess.