NWN's original single-player campaign may not have been very inspired, but Morrowind's was an undead puppet in comparison, as far as being lively.
It was Fed-Ex training VR software for a medieval world full of cardboard cut-out automata.
From my perspective, the original NWN may have been mediocre in single-player, but the whole point was to provide an extensible multiplayer framework -- and the community has gone to town over it. The persistent worlds online are amazing, and there are user-created modules of such high quality that it's worth buying this game just for those.
HotU will build on that, improving it in many ways by providing players, DMs and creators many new possibilities.
There has been no other game like this. It's like a mix of the best aspects of CRPGs with elements of MMORPGs.