Woah, woah, woah, WOAH! Don't lump me in with the other NWNers that are dumping on DA here! I love DA (and I pre-ordered DAII).
I also love NWN (is that a given? Well, it should be!).
As has been mentioned before, NWN represents the epitomy (at this time) of a complete RPG package for the PC. Nothing comes close to it. Presently.
DA (and DA II) are, IMHO, the best SPCRPGs (single player computer role playing games) available presently.
Thus, they are really not the same things - though one can compare them to one another in their catagories.
In SP, DA wins hands down.
In Toolset, MP, DM Client, etc, NWN kicks butt.
The end.