I've read it peripherally, so here's my first impressions.
What I expected: A location book giving details on XenDrik's history, culture and locations.
It delivers for the most part on cultures of various drow and giant types, not in depth but enough information to make using them useful.
It delivers in spades on locations. You get specific locations (such as City X and Ruins Y, featured on the map, then detailed in the text, including Stormreach and a few towns) and you get generic locations very evocative of XenDrik's flavor.
It falls flat on history though. Everything is scattered and rumors, and they generally stick to generalities and "mystery". That's more about my expectations than the book though.
What it delivers that I didn't expect, was adventures. It's got lots of adventure fragments, with a location and basic plot. Some of them can stack togethor into a minicampaign. Very interesting.
The Umbra-whatsit drow are mentioned, but you're refered to Dragon magazine. It also includes Shattered Lands stuff like the firedrow.
PrC's didn't do much for me, didn't read all the magic items or monsters yet.
I do like the noble/couatl Yuan Ti though, very nice idea.
Also, yeah, Warforged were made by Quori (in a construct way, more than a living construct way) and Docents were a method of trapping quori, or something of the sort. Cainnith looted XenDrik for the 'forged. The interesting thing is, since Dal Quor has rebooted since the invasion, the Dreaming Dark is not previously aware of the connection, but is also plumbing the depths of XenDrik for secrets of the war.
All in all, a great "kit book", very useful, though not the Xen Drik sourcebook I expected/wanted. Still worth the money.
And, MM4 is a good book too, don't let the haters spoil it for you!
