Yeah, NWN2 is known for having a very un-optimized engine. But hey, it's Obsidian, what did you expect?
NWN2 is full of flaws, but it has redeeming qualities as well. And compared to DA2 it looks like a great game. What doesn't? :D
NWN2 OC is worth playing once - it's generally tedious but has some neat elements. Just be warned, if you think Neeshka is annoying, wait till you meet Quara. And don't ask too hard why you have to spend 10 hours questing to get a certain locked door to open. And... nevermind, you'll see for yourself
I replayed it twice (to check out both good and evil aligned quests and companions), but the second playthrough was definitely not worth it.
MotB is the best non-indie Western storyfag game released in the last X years, and it's often considered "Torment-lite". It's set in Rashamen, so the world is definitely much less cliched than the western part of Forgotten Realms. The best of the lot as a "proper" codexian RPG experience.
SoZ is quite different, more like a "spiritual successor to Icewind Dale" - create your full party, wander around the Realms, follow a loose main quest and look for unrelated mini-adventures on the world map distantly reminiscent of HoMM... :D
NWN1 is different, and the engines are not compatible (so expect crappy 3D graphics from 10 years ago). Before DA2, the NWN1 OC was the worst thing Bioware ever released, now they rank about the same for me. The more of it you skip, the better.
SoU is not as bad, and it's nice to see a proper low-level experience. However, it's really nothing special and I can't imagine why would anyone want to play it more than once.
HotU is a good dungeon-crawling epic level romp, even if the munchkinism gets ridiculous at times. As other people have recommended it before, I won't go into details
As for user-made modules, the NWNVault Hall of Fame is a good starting point for both NWN1 and NWN2 modules, and there's some great stuff there.