I do love Neverwinter Nights, and consider it to be one of the best PC games released in 2002. I'll give you a real brief rundown of what I liked and didn't like about it.
What I Liked: A mostly-faithful translation of the 3rd Edition D&D rules. Incredibly addictive multiplayer mode if you have friends who also own the game, and it gets even better if you have a DM. The sound effects and music are very good, and the Aurora Toolset allows unlimited potential for custom campaigns and modules. With new modules coming out all the time, you could be playing this game for years and not run out of stuff to do.
What I Didn't Like: The single-player campaign is rather dull, with most of the quests boiling down to "Retrieve this item and deliver it to this NPC". The single-player campaign is also linear, and you don't have many choices in what you can do. Of course, I've probably just been spoiled by the Baldur's Gate games, which had excellent single player campaigns. Another (small) gripe is that NWN's graphics engine is a little dated, but that's something I can easily live with.
There are the pros and cons. If I were to rate NWN, I'd give it a B+. It suffers a little from the lackluster single player campaign, but the multiplayer and customizability options more than make up for it. I consider this game a must-own for D&D fans (or RPG fans in general) who like multiplayer games.