I've read quite a bit of Dawkins' work, and I never get tired of him. Reading his books is intellectually exhausting; I often find myself having to reread sections because my eyes glaze over. Not because it's boring: just because there's so much. But Dawkins is engaging, even funny, and every page bubbles over with his excitement about what he's talking about. Dawkins loves his subject, and he's a genius, and that's evident everywhere.
I liked the format of this book quite a bit: it seems odd, but actually it's very natural. For one thing, it breaks up the chapters into quite short sections, each of which focus on something particular about a species that has joined our trip. Sometimes it's something unique about that animal, something that makes a point about evolution in general or that's just really, really interesting. Sometimes it's an excuse to talk about how we know what we know, like how scientists date objects or how we decide what goes where on the tree of life.
Part of what I liked so much about this book is that Dawkins is never afraid to admit where he's walking on shaky ground. He freely points out where the science is weak and explains why he went with the theory he did. (This is how you can tell a really good science book from a mediocre one, by the way.)
This is a long book, so unless you're interested in evolution, I wouldn't recommend it. Dawkins also makes digs at creationists here and there, but only because they're so fond of taking his words out of context. That being said, if you're already a fan of Dawkins, you should definitely check this one out. Despite its length, it doesn't really tread on the ground that his other books have: it references them, but most of it is completely unique to this book.