The best OC for the original Neverwinter Nights, but that's not really saying much.
Hordes is a pseudo-sequel to Shadows of Undrentide, featuring the same protagonist but an entirely new "plot line" that is in no way related to the one from Shadows. Essentially your character starts off in Waterdeep with no explanation on what happened after he or she fell into the Plane of Shadows. They are in Waterdeep after hearing about a call for heroes.
Apparently the Drow are getting uppity, and are attacking Waterdeep via Undermountain... an always changing dungeon owned by the mad mage Halastar. Hordes is split into three chapters that practically have nothing to do with one another, Hordes is essentially three mini-stories in one game. Each chapter has a different antagonist, setting, and storyline making Hordes feel, in my opinion, very disjointed. It's not a bad campaign, it has its positive points, but it feels like three different plots sloppily thrown together. The stories themselves are not particularly remarkable.
The campaign may be a bit disjointed, but the new content added in Hordes makes it worth the price of admission for module builders and power gamers. You're now able to go up to level 40 (as pointless as that is), and there's new classes, and prestige classes. Module builders also get some new very well designed tile sets, monsters, items, etcetera to choose from.
For me Hordes of the Underdark has always been a hit and miss title since I first played it when it came out. Replaying it, I feel the exact same way. The campaign has its good points, but it feels disjointed, and the storyline is not anything remarkable. Still, the new gameplay features and toolset content can be fun to make use of.