Dawkins has written other books about evolution but at over 600 pages this goes over the subject with a fine tooth comb. It is loosely organized like Chaucer's Canterbury tales. If you are a science geek, you'll enjoy this.
This book is not for the faint of heart. It's a massive biography of the human race that begins in the modern day and traces our ancestry backwards to the beginning of life itself. Along the way it takes many detours, and many other species have a chance to tell their own tales, each of which provides some lesson or insight on genetics or evolution. It's written in typical Dawkins style; if you enjoy his other books, you'll like this one too. His gift for explaining the most complex scientific concepts in such a way that any layperson can understand them makes this book an easy, if long, read.