I've read so many of his works (at least, his usual fantasy novels) that I feel like I've learned all his tricks. I no longer feel surprise at what he writes (again, excluding what I'm reading now, which many people consider his crowning glory).
The feeling that I know all his tricks, so to speak, doesn't change my opinion of him as a writer, though. I think he has excellent, well-executed ideas and throroughly built worlds. I adore the fables and storytelling within his stories. My favorite part of the Sandman series thusfar is at the beginning of The Doll's House, when two men wander into the desert and we hear of Nada, Dream's former companion. The conciseness of it is awe-inspiring.
Knowing his style so well is actually comforting. It means Gaiman is human. It means my understanding his writing could make me as good a writer as him someday.