This is one of the best D&D books I have read.

The setting, Thay the dominion of the Red Wizards, is very interesting and the author makes the best of it letting us peak into their cities, their customs and their people's day to day lives.

The characters are almost all well developed and memorable. We get to see lots of dark wizards, specially necromancers and clerics of the evil gods like Bane. A large parade of unusual creatures like Nighthaunts, Tanar'ri and Quells make an appearance mostly as the antagonists of the story.

The only shortcomings I see are the constant jumping among too many story arcs at the beginning of the book and the abrupt ending, that makes reading the sequel indispensable.