TheElegantUniverse begins with the standard boilerplate, the introduction of special relativity (the logical structure for which is amazingly simple but for which the concepts are equally deep), general relativity, quantum mechanics, and some particle physics/introduction to the Standard Model (other texts talk about Newtonian mechanics and electromagnetism, too). I mostly skipped this portion on this reread, since while I don't claim to deeply understand the topics in question, I am familiar with the typical introductions. Then, Greene starts digging into the meat of the topic, covering the history of string theory. He starts with the accidental discovery of the Euler beta function and the attempt to use string theory to explain the strong force, which was ultimately superceded by QCD. He then digresses to a discussion of supersymmetry and why it is important, followed by a discussion of Kaluza-Klein and extra dimensions, and how they relate to string theory. Finally, he then catches main thread back with the creation of true superstring theory and the first superstring revolution.
This is the natural and quite typical organization of books on the topic; though well-written and organized, I would not call it exceptional. Where TheElegantUniverse shines, in my opinion, is that it delves into some of the meat of the theory: how the additional six space dimensions are curled up into Calabi-Yau manifolds (a word Greene avoids in the text), space-tearing transformations (which I have nowhere near enough topology to understand at a deep level), so-called mirror pairs of Calabi-Yau manifolds, how perturbation theory relates to string theory, possible experimental evidence, connections with black hole physics, and speculations on string cosmology. The section I found most interesting is the one which details how duality relationships on the string coupling constant and the way reveal that the five separate superstring theories are related by dualities into one larger theory, called M-theory.
TheElegantUniverse is a surprisingly thorough overview of its topic, presented at a reasonable level. It is probably not my favorite book on the subject (I would give that to Steven Weinberg's DreamsOfAFinalTheory? because of that book's sheer elegance), it is probably the most informative. While I have been somewhat skeptical of string theory in the past, TheElegantUniverse, other books, and the increasing interconnection of string theory with other topics in theoretical physics have increasingly convinced me that string theory is probably on the path to a final theory, even if its current incarnation is not correct.