I'm writing this review as much in response to the other reviews as I am in response to the book itself. I feel the other reviews are misleading as to what this book is and what this book isn't.
First of all, please be aware that if you wish to read this book, clearly marked volume two, then it only makes logical sense to read volume one first. You will not understand this book if you do not read the first volume, Primitive Mythology, beforehand. It's that simple. Campbell weaves an ornate tapestry with this series, and you have to start from the beginning of the thread to see how it all weaves together. Moreover, he introduces many invaluable foundational concepts in the first book that he uses in the second book without redefining, because he's assuming that you read the first book. If you didn't, then that's your burden to bear, and not Campbell's.
Second, this is a difficult book. I'll just put it out there right now. If you're expecting an easy-to-follow textbook on the basic stories and myths of these cultures, then you're reading the wrong book. This book is not an enumeration of major myths, but rather an anthropological and philosophical analysis of the flow of concepts and ideas that gave birth to those major myths. This is not a book merely of "what," but also of "why" and "how." I'm not saying that you have to be familiar with every major myth of every culture before reading this wonderful series, but it does help to have at least a cursory understanding of the major religions and mythologies. Campbell does a great job of concisely relating the basic points of the myths he's discussing, so there's really nothing to worry about, but just be aware that you're not always going to get the play-by-play, and if you're looking for that, you should consult a different book.
Continuing with the fact that this is a difficult book, I will also say that the language and the arguments are quite advanced, so be prepared for a book that's intellectually challenging, rather than summer reading. You get the hang of it after a while, but definitely skim some pages of the book before buying, to see for yourself if you'd feel comfortable with the reading level of this book. Personally, I'm OK with reading it in just about any season, but maybe that's just me.
Now that I'm done ranting, I can get to the fun stuff. The biggest reason why you should read this series? It will change your life. It will reveal new histories and modes of thinking to you that you never thought existed. It will show you firsthand the story of humanity, in all its victories and tragedies, and more importantly, in all of its interconnectedness. All of mythology is different variations on the same theme, as Campbell shows. You can also tell just from reading how excited Campbell is about the whole subject, and his sense of awe and wonder, present even after spending his entire life studying this strange story we call mythology, will definitely rub off on you. I've realized things about myself, about humanity, and about life that I never would have if I hadn't have read these books. Please, do yourself a favor and read these books, but just like the mythological hero as of old, proceed only if you're ready for the challenge and adventure! (And not to mention, if you're ready to buy volume one, first!)