I thought the first campaign was so-so, the first expansion pack was more or less the same. I really did enjoy playing the second expansion pack, especially after you enter the Underdark. The Hordes expansion was one of the few RPGs where I thought the evil side of the game was more fun than playing the goodie. Plus, if you do the evil side, there is great, though short, series of player modules (
The Gods Themselves Trilogy, be warned there's a spoiler for the evil ending in the description) that take place as a sequel for an evil HotU character.
And speaking of which, the player-made content is by far the best thing about NWN. For starters there's the
CEP, a huge mod that contains tons of additions, including new weapons; new monsters; new clothing; tons of new objects; more character animations; mounts; flying; other graphics; shields with heraldic crests; and absolutely best of all, capes on armour.
After that, there's the ton of utterly brilliant player-made modules available. If you're interested, start
Here, as virtually ever module there is of top quality. If you want something a bit less High Fantasy than your average D&D Campaign, I'd highly recommend
The Wanderer. As much as a game set in a world with wizards and dragons can be, it manages to be very realistic. Nobody knows you at First Level; quests which NPC's say are time related actually are, as opposed to like normal RPGs where something's only time-related if there's an onscreen countdown, regardless of what people say; your main concerns are surviving rather than saving the world,; etc. etc..
Other than that I'm not sure what else I can say.