A lot of people crapped on The Postman, and while it's a heavily flawed movie, I have a lot of respect for Costner in trying to make a faithful adaptation, in both spirit, and, er, letter, of the original David Brin book. It's no masterpiece, but it isn't a disaster either.
I liked Postman, and I liked Waterworld, too...haven't read Waterworld, but Cosner can capture a certain tone pretty well. I'd like to see him tackle Norman Spinrad's Songs from the Stars. When I read it, Clear Blue Lou has Cosner's face in my head...