The philosophy underlying the previous edition stays the same. The presentation of concepts is rigorous but neither difficult nor trivial, suitable for readers with basic notions of linear algebra. Moreover, new material has been added.
Chapter 3, which deals with block ciphers and linear and differential cryptoanalysis, is very well-written. This is the best presentation of such a subject in few pages I have seen until now.
Chapters 4, 5, 6 and 7 have been significantly updated and expanded with concepts and techniques that are fundamental in order to understand current researches and state of knowledge in Cryptography (e.g., random oracle model, semantic security, new attacks against public key cryptosystems, an in-depth introduction to elliptic curve ...).
Compared to the previous edition, more emphasys has been given in some parts to security proofs (e.g, chapter 4), and several new exercises have been proposed at the end of each chapter.
Other readers have pointed out that there are some typos (the author has made available an errata list on his home page) but I think that the value of the book is not reduced in any way.
In my opinion it is a great book for people who want to be introduced to problems, ideas, and techniques used in Cryptography.