What a heartbreaker. I really used to love his stuff and will still insist that series like Incantations of Immortality, Battle Circle and Bio of a Space Tyrant are well worth the read, but once I read Firefly I just couldn't stomach any more of his work.
Have you read the Chroma series? It ruined me for him. I was so sad. More and more sex with more and more age-inappropriate people, until the third or fourth book where the guy starts up on having sex with his underage daughter. I was done.
I will always love the Incarnations and the Adept series, though. And the first 20 or so Xanth books.