Hyperion by Dan Simmons. I had an itch for some good epic world-building after finishing the Game of Thrones books and giving up on the next ones being released. Was not disappointed.

Structurally, Hyperion is a play on Canterbury Tales, but it weaves in hefty amounts of sci-fi, fantasy, philosophy, history and theology. Lots of WTF moments, and a great balance of humor and truly dark shit.