An amazingly lucid book evenly dealing with different approaches to unify quantum mechanics and general relativity in a theory of quantum gravity. Smolin is very straight-forward and presents his ideas in an interesting, provocative and intelligent manner. I've struggled to understand how space can be quantized for three months, and I think I finally have some solid explanations. Smolin also does well with the Holographic Principle, which is about a difficult subject as you can come by in modern physics. The main reason I bought the book was for a clearer understanding of Loop Quantum Gravity, which is Smolin's specialty. Sadly this is the one chapter that I felt was lacking. I don't know if it's the subject, or just Smolin, but every other approach to quantum gravity was very easy to understand in plain terminology. Perhaps he's so close to the LQG approach he doesn't know how to give it a non-technical treatment. Moreover, the chapter is filled with anecdotes that detract from the presentation of ideas.
I liked the fact that Smolin proposes an open mind for both the general public and the community of theoretical physicists in the pursuit of a quantum theory of gravity. He rightly asserts that the practice of jealously guarding one approach over others rather than an open approach to all methods is stifling and will only hinder scientific progress.