Wow, what a wonderful, wonderfully varied array of responses.
I have been lurking for a while and not posting, among other things because I was just too busy to put together a proper post.
There's one thing I want to add, though. The Thoth is the ONLY deck I was able to read with off the cuff, as a newbie. Beginner's luck? Perhaps. I have a theory, however. I think Crowley designed the deck to engage your senses in a way that no other previous deck ever did, and that's why he gave free reign to Harris, with her swirls of vivid colors and her sacred geometry studies.
Pixie's drawing hand is a lot surer and more competent than Lady Frieda's, but her art is remote, sedate, static, meant to be observed and decoded. It doesn't jump and grab you, and, whatever its virtues, it's definitely not sensuous. Where Waite and Smith keep it clean and simple, Crowley and Harris throw in everything and the kitchen sink. Compare any card from their decks (the Lovers is one that quickly comes to mind) and you'll see what I mean. These are very different mindsets at work. One is subtle and guarded, the other is definitely nothing of the kind.
What I'm trying to say is that I think Crowley intended his deck to be picked up and read, no blinds, no questions asked. The depth of the reading would depend on the reader's preparation.
It doesn't explain why it's so closed to me now --although ravenest may have a point, or at least I hope that's close to the case here
.
" He who knoweth little, thinketh he knoweth much; but he who knoweth much hath learned his own ignorance. Seest thou a man wise in his own conceit? There is more hope of a fool, than of him. "
http://hermetic.com/crowley/libers/lib30.html
I HOPE. Although I don't think I have the full measure of my own ignorance yet.
And I think this is probably the best, most succint description I have read of the Thoth, bar none:
Like Bruce Campbell as "Ash" with his boom-stick, it's just saying "Come get some!"