An excellent book! I highly recommend it. You should probably read "Prometheus Rising" first, though, as it's easier to read and comes first. But this book can still be read on its own.
Laced with Wilson's typical weird humor, this book is a mostly serious work explaining Wilson's proposed philosophy of quantum psychology. A complete rejection of Aristotle's either/or thinking, quantum psychology has much in common with Existentialism, Operationalism, and the Copenhagen interpretation, showing how the weirdness of quantum mechanics cannot be avoided in our daily lives (we just tend to not see it, or ignore it), but manages to NOT lapse into solipsism. Wilson posits that 1. There IS an Ultimate Reality beyond our perceptions, but 2. We humans will never be able to experience it directly, because our brains don't actually tell us what the world looks like: it makes a guesstimate based on a tiny portion of possible sensory data. Even with instruments to tell us things about the world our 5 senses can't, we still will always experience only the model of reality we have built in our head, not the real reality. The brain is a blind king that thinks the contour map his servants made of his kingdom really *is* the kingdom. We keep thinking the map is the territory, but it isn't. When you see, say, a book or a chair, you're only actually seeing your brain's best guess at what a book or a chair looks like.
Wilson manages to keep away from the treacherous waters of solipsism by occasionally reminding us that though we can only know the map, the territory is real. So we are not limited to either "all we see is real" or "nothing we see is real." There is still statistical probability on our side, and we can be as much as 99% sure of certain things... just never 100% sure.
What's best, in my opinion, is that in the foreword, Wilson gives us brief but complete summaries of philosophies and philosophers important to the rest of the book, for those of us who aren't philosophy majors. There are also exercises at the ends of each chapter, apparently for groups of people to read chapters and then do the exercises together.
This is one of those books that is a fascinating read every time, and I get something new out of it each time I re-read it.