for me, his stories have always had a great balance of science (real or skewed) with fantasy that make you believe in the possibility of his words. that's why i love science fiction, it makes you think and forces you to imagine the consequences of how we live, naturally and artificially. his final book, "Next," deals with biotechnology and is one of his best.
one of my favorites, though, is his non-fiction book "Travels." i appreciate the wanderlust we shared.