Brian Greene is likely passionate about his discipline and we feel that he wants to take the reader by the hand to show him the fortress of modern physics. The Elegant Universe offers a ride of 600 pages from Newton to string theory, superstring theory and M, via Einstein and quantum physics. It is rather successful: the author puts at the range of an average player and tries to find a talking analogies. Sometimes he repeats, sometimes it aligns more examples that may be required, but the one in the other it pays and we understand what is happening. Next, in terms of the validity of string theory whose author is a strong supporter, it is difficult to judge without the game. This distance put, it's good book extension, standard class.
Note that there is a documentary shot of this book (same name), available on DVD.