Not really on par with BG2 or Planescape in single player, but still very worth a play. NWN really shines when it comes to multiplayer (which it was designed for really)
I would wait until the deluxe editon comes out, so you get both expansion packs. The campaign that come with those are way better then the one that comes with the game alone.
as Warbie states,if you havent played the baldurs gate series or planescape torment, start with them. Neverwinter nights was a bit dissapointing in my opinion.
Or if you are the type of person who will only play "3D" games then go for knights of the old republic, its a winner.
Neverwinter nights is well worth playing, but unless your a role player, dont think your going to get vast playtime out of it, as far as mods good, there not bad, the single player ones tend to be short, but there are alot of great RP servers online, I play on one of em.
If you buy nwn, and both the addons, you got alot of playtime, it will last you a long long time.