Just finished reading it. It's fine. Not great, not thrilling, but a good solid intro that sort of makes the Banzhaf books redundant.
It's definitely a supplementary book, and it does expect you to know certain things without having explained them: basic Qabalah, alchemy, and astrology, the concepts of Aeon, Thelema, Nuit, etc. But it would be a good textbook for a class. In fact, that's what it reads like: a well-organized textbook by someone who's an educated fan of the deck.
IN a way, I feel like it's the kinnd of book that keeps being produced for te Waite-Smith over and over and over: a more-than-cursory look at symbolism, attractive tables and graphics, meanings... So that either means that Crowley is officially mainstream, or else Llewellyn realized that there is a group of people who want to use the Thoth for divination but can't find a concise keyword/symbolism guide. It IS a great compliment to the Duquette (especially since Lon isn't always thorough in his look at the individual cards).
As you say: not blown away, but perfectly happy to own and have read it... and I'd definitely recommend it in some cases.
Scion