here on Amazon. The first thing you should know about this book: it is about philosophy. It's not about theology, or what do Pagans believe; it's not a book to help you go more in-depth with your practice or to hammer out the finer details of your personal world-view. It is a philosophy text written in the traditional style of persuasive argument; in this case, the argument for polytheism.
John Michael Greer is the current head of the Ancient Order of Druids in America, a group I don't have much personal experience with but have heard good things about. He is also a prolific author who has released many Pagan and esoteric titles, and maintains his blog, The Arch Druid Report. This particular work is a bit of a departure from other things I've read by him; his tone, while remaining conversational and easy to read, is very much rooted in the philosophical tradition.
In the first part of the book, Greer outlines his basic arguments for polytheism, as opposed to either classic monotheism or atheism. Though the first half of the book does seem to largely digress into discussions of the various arguments for the aforementioned positions, I for one appreciated the basic overview of these classic arguments before diving into Greer's own counter-arguments. He makes many persuasive points; the main argument being that with so many different experiences of the sacred or deity, it therefor makes the most sense for there to actually be different deities imparting these separate experiences. He also addresses many of atheism's arguments against theism, and many classic monotheist's arguments against atheism and (misunderstood) paganism, and quite handily shows their inherent flaws when faced with a polytheistic worldview.
I personally greatly enjoyed this book; but I also minored in philosophy at the undergraduate level. Those more unfamiliar with the discipline of philosophy, or who are familiar but don't enjoy the type of arguments that philosophers frequently entertain, may find this book much less appealing. For the Pagan who is often faced with religious debates or attacks by Christians or atheists, this book can arm you with some very valuable, perspective-changing arguments that may be of great use if you are interested in engaging in those kinds of discussions.
Overall, I feel this is a very specialized piece of writing that will probably appeal to a small group of the already small group of Paganism; but if what you've heard sounds appealing, you'll probably enjoy it a lot - I certainly did!