The movie is a major rewrite of the book. It is built on the frame work of the book but leaves out much of the humor, dispatches characters, ages the principal players and replaces any subtlety with far more violent action. I don't think it was a real improvement.
However, it does have terrific effects including a centaur, minotaur, satyr and hydra. The centaur Chiron is just about the best one ever executed and is played by Pierce Brosnan. There are only fleeting glimpses of Chiron and the black satyr in this trailer. We'll have to wait for the DVD release to see more.