Epic levels (and all the feats that they entail), new prestige classes, two henchmen (with interaction between them a la BG, and the possibility of PC/henchman romance)... There are some craft skills, such as for weapons and armor, and so you can make mithril weapons, etc. There are dye kits for your armor so you can customize the look of it.
And, as with Shadows of Undrentide, the new prestige classes, feats, and skills will be available in the original campaign... which means I will probably play it through... again. Maybe a Shifter.
So, uh, yeah, I'm really, really excited, if you hadn't noticed. But then again, I liked NWN and Shadows of Undrentide quite a bit, so I'm eager for this sort of thing that lengthens my NWN experience with Cool Stuff.