If you enjoy games based on the D&D ruleset then I would definitely recommend NWN. As you've heard others mention, the original campaign is thoroughly mediocre, although the two expansion campaigns (SoU and HotU) are decent enough. Also, something to understand about NWN mods is that you're not actually modifying any of the official campaigns, but rather are loading up entirely new modules to play through (basically providing near-unlimited gameplay, due to the large number of quality modules out there). A good place to start if you go looking for modules would be
this thread, as there are quite a few real gems in there. My own recommended order for someone new to NWN is to skip the original campaign, play through SoU and SotU (as these are decent and will give you a good introduction to the game), then jump into whatever user-made modules sound appealing to you.