I tried it out in STO (I haven't played NWN but from what I understand it's the same, more or less). I was never a mission creator type in any game, but it wasn't all that bad, as I recall. The missions that are made from it obviously run the gamut from bad to really great, but the really great ones are really, really great. I don't know if NWN has the same type of creator community STO does, but you can see tutorials for STO's version, as well as many of the great player-made missions, here:
http://starbaseugc.com/