This book contains three stories: The Crystal Empire (PZB), Onion (CRK), and The Rest of the Wrong Thing (PZB & CRK). The stand-out among the three is "Onion." It's fascinating and as close to perfection as you can get. The more you read it, the more you see and understand. Definitely one of the best stories I've ever read.
The illustrations by Richard A. Kirk also make it worth checking out.