Although technically, this is a science fiction novel, not a fantasy, even though it reads like the latter... But I guess you could say the same for the Coldfire Trilogy and probably several other books you've got listed as fantasy.
Anyway. AMAZING book, but I would probably put in the Top 10 SF books list instead.

Roger Zelazny is far an away my favorite sci-fi author, and this might be my favorite novel of his. I have re-read it several times, which I usually don't do with books, and more than that have read it back to back to back in a weekend. An amazing blend of sci-fi, fantasy and philosophy.And to top it off, it has one of the best/worst puns I've ever read ... "Then the fit hit the Shan."