I'm reading through it in detail, and I've found it to be firmly mediocre to satisfactory.
I found the entire first chapter (drow society) to be very good, and to be quite consistent with almost all the previous material written about drow, whether it was from GH or FR (albeit with a heavy focus on Lolth). As Ari pointed out above, a large amount was covered, including a lot of the oddities. I was very satisfied with this chapter (though I still prefer the FR material the best).
The other chapters are okay. The character options were okay to poor, with most feats being interesting in concept but very weak in mechanics - I can see few DMs creating drow villains using more than one feat from this book when the PHB2 and Complete series exist. There were a few gems, though. The prestige classes were "meh", again being very weak. The concepts were reasonably interesting, however.
The maps, though, brought this book down horrendously for my personal taste. Other than the city map of Erelhei-Cinlu (which was great), the encounter maps are horrendous. Ugly blotches of color over a completely uninspired "arena"-like open space with random lines/walls scattered about (and called a "villa" - no, it sure as hell is not a villa). I understand now that these maps are from the Fantastic Locations (there's a misnomer if I ever heard one) series of DDM maps - I can now see why that series has sold poorly (according to that roundtable with WotC staffers). Holy crap, do they ever suck. Their appearance in this book was not appreciated.
Good maps = Christopher West's Maps of Mystery. Bad maps = Fantastic Locations.
Overall a satisfactory book, and I would make the purchase again.