The article at IGN contains a great deal of info on the DA2 demo. The article goes into more detail on the plot of DA2 as well as info on some new characters (including Hawke's family). There is also some info on the new dialogue, combat, and leveling systems.
I should warn you all that the article has some possible spoilers in it (more so than many other articles on the demo). I was honestly surprised at the detail in it compared to other articles I've read.
Click here to read the whole thing here.