When I started reading this book, my first reaction was, "Wow, what great atmosphere!" Egyptian magic, Coleridge, eighteenth-century England, secret societies... atmosphere abounds. But the thing about atmosphere is, it works well for the first half of a book, when the writer can get by with obscure intimations; but eventually, the book has to let you know what's going on -- and that's the point when many atmosphere-heavy books dissolve into an inchoate and incoherent mess. Because while it's easy to throw together a bunch of really cool elements and hint at secret plans and intricate plots, it's a lot harder to tie all those disparate elements up with all those ominous hints; and it's harder yet to make the revealed story live up to its veiled promise.
I stress the difficulty of this task, because it's all the more remarkable that Powers pulls it all off. The time travel, the mysticism, the historical figures -- it all works. When Powers finally pulls the veil away, what's underneath is just as intricate and rich as the reader has imagined -- and it makes perfect sense. That's an impressive trick indeed. This is the kind of book I really enjoy: it's complex enough to rise above the level of fluff, but still possesses the pace, wit, and joie de libre that make fluff so attractive.