I have read only about a quarter of the book so far and it justifies the reviews I've read. Despite the one or two reviews suggesting this book is only for the layperson, Professor Susskind takes the reader through the various stages of the mathematics (proofs) necessary to achieve a clear understanding of what is a very profound and abstruse subject. As the man said, "the beauty of quantum mechanics is in the mathematics: just follow the maths." I would  like to add, though, that if the reader's maths don't go beyond say GCSE level, the explanations given will seem like learning a foreign language; so not a text for the faint hearted.<br>If I do have a criticism, it's the interludes of supposed humour which frequently punctuate the text: the book doesn't need it and it doesn't add anything to the overall presentation: that's why four stars have been awarded.<br>But don't let what I've written detract from the quality of the book; it's well written, the author clearly knows his subject, and the book's price is very reasonable. So if you've an interest in this direction, whether as a student or layperson, go for it -- I don't think you'll be disappointed.