Absolutely great. Skips the whole introduction part that is quite boring in most books and jumps straight into fast-paced action. Dazzling from start to end.
Before Lestat accepts Memnoch's offer, it's as thrilling as the best moments of the other books in the series.
After he does that, it's so thought-provoking that it may feel overwhelming. Anne Rice offers, through Memnoch's explanations, an incredibly logical and reasonable theory about the creation of the world and the higher planes of existence. Putting parts of this next to my own theories, I can finally see a reasonable role for a being assuming the role of the Devil. Of course, there are also parts that I wouldn't even consider as possibly true, but it's one of the best such theories I heard of so far.
And the end is baffling. I can see more than one way to interpret it and I'm very unsure which one to pick. What was Maharet's role in all of that? What was the real point of everything? Where did everyone go at the end? How many are left?
I know one thing: I'll miss Lestat, since as far as I know the books that come after Memnoch in the Chronicles are, just like all the books in the New Tales of the Vampires, stories "written" by David Talbot about the lives of individual vampires, and Lestat has almost no role in them.