It was an easy read and I should be giving myself 3/5 stars instead of the author, for picking up a book that was not something I would enjoy as much as some other book. Still, I read through it to double-check on myself with regards to understanding of certain physics phenomenae. The book should be read by someone barely starting to venture into the world of physics and cosmology, a teenager perhaps.
My 13 yr old son devoured this book in 2 days so it is an appropriate juvenile level. He didn't love the biographies of the scientists involved in the discoveries but loved the explanations of the theory.