I just finished
Lord of Light by Roger Zelazny. Brilliant. It transcends science fiction, deep into religious and metaphysical territory, plus fully realized characters and engrossing dialogue.
A choice quote: "If the world were all city, he had reasoned, the dwellers within it would turn a portion of it into a wilderness, for there is that within them all which desires that somewhere there be an end to order and a beginning of chaos."
Ninety-eight reviews on Amazon averaging five stars.