If you read books on physics, then chances are you have read some of Stephen Hawking's other books. If you don't read physics books, then this is a good place to start. The book isn't very long. I read it in just one afternoon. However, part of that is because I could not put it down. It's similar to his condensed and updated version of A Brief History of Time, called A Briefer History of Time. This time, however, he delves into a little philosophy. It's funny, because he says in the opening of the book that philosophy is dead. However, I think he's talking about philosophers of mind and theologians who do not keep up with the most recent advances in science. So don't fret, philosophers. He does put forth a very logical positivist style philosophy of science called Model-Dependent-Realism. It's an interesting concept. Furthermore, the focus of this book is M-Theory, which many know as string theory. The difference is that there are many individual string theories, and theories that are inspired by string theory (take the Randall-Sundrum model for instance). M-Theory is the collective name for all of these. Some might say that Hawking is a bit TOO convinced of M-Theory, since there is not, as of 12/18/2010, much experimental evidence to back up it's more outlandish claims. Hawking draws the conclusion that there is no need for a creator god because of the physical laws discussed in this book. I, of course, agree with this. However, that's up for the reader to decide for themselves. Even if you are a religious person, there's not much of a need to get offended over this book. For a person interested in physics, it's an exciting read on the modern state of physics. However, I would recommend reading another book by him to supplement this if you are not familiar with physics.
I give it an 8 out of 10. I'd give it a higher score, but I would have liked it to have been a little longer. Another point off because Hawking seems too convinced of a theoretical model that is still incomplete both mathematically and empirically. Nevertheless, this is a good, thought provoking, and informative read.