It's mediocre. The first chapter is fantastic IMO, giving very good details on drow society and culture that is reasonably consistent with everything that has come before (including why drow dress the way they do). The only disappointment is the lack of detail (pretty much not even mentioning in any noticeable degree) on all the other drow deities. (Though this only slightly disappointed me, as I own all the FR drow-related material - and the FR drow are the superior versions. Yeah, that's right, I went there.)
The feats were okay to poor, with only a couple worth giving to drow antagonists, and the rest being woefully weak and worth only ignoring, IMO. The prestige classes were all underpowered (again, totally IMO) and I'll likely never look at them again. The feats worth taking were cool, though. The spells and magic items are also decent.
The maps were universally terrible - except, luckily, for the map of Erelhei-Cinlu itself (whew!). The rest are just the FL series maps, which are simply blotches of color and some random lines. Ugly, boring, and useless. Christopher West's Maps of Mystery from Dungeon (hell, anything from Dungeon) are vastly superior in every single way imagineable. Wow, DotU had terrible maps.
Final note: Use of the idiotic internet-speak "buff" word was used in this published hardcover. Hey, whichever author vomited that out: improve your vocabulary, sparky.
[Sessler]A 3 ... out of 5.[/Sessler]