I had the opportunity to receive and review this book as member of O'Reilly blogger review program.
As experienced IT Pros, we are facing one issue every time when product vendors launch new version of product or technology which we use during our everyday work. The issue is: how to catch all new functionalities as soon as possible, so that we can benefit from them in our future projects. One approach, for sure, is to attend conferences and learn from sessions presented by product groups members, but my finding, both as conference speaker and as attendee is that conference slots are quite short for this amount of new information, and that as an attendee you can easily forget what you have heard on one session at the exact same moment when you start to listen next one.
In my opinion, that is the point which is completely "scored" with this book. The book is one comprehensive resource that introduces and describes all of the changes and new features which are brought to us in SharePoint 2013, all condensed to 200 printed pages. Starting with improvements in architecture, continued with Search, Enterprise Content Management, Social, Composite Solutions and Business Intelligence. Book is not too long, and cannot explain all of the mentioned improvements in depth, which of course cannot be expected from book that has "Exploring" in its title. On the other hand, book is conceptually organized in a way that makes it good reference guide which can be used every day for quick introduction to improvements across SharePoint 2013, and use plenty of provided reference URLs to directly (at least from eBook edition) jump to some web pages which cover book topics in more depth.
In any case, you should familiarize yourself with Chapter 1, that covers improvements in Architecture, which is also provided as free download on book webpage on O'Reilly. Other Chapters, after first read, can be used as quick reference to new functionalities you can leverage in your projects depending of its purpose. I would recommend this book to all IT professionals which already have experience with SharePoint 2010, and highly recommend to all SharePoint architects.
Official book page on O'Reilly web site: http://shop.oreilly.com/product/0790145372888.do