There are a couple of things about this book that I REALLY like. First is that it is a good learning tool. It starts with some really basic Python code (an insult generator), advances to something more advanced (tic-tac-toe, from 2 player to an intro to AI) and for the most part continues with this pattern throughout the book. Getting a little more advanced with each turn of the page. (The exception to this comes in the hardware projects, where some of the earlier projects are harder than some of the later).
This book also does a pretty good job, most of the time, at explaining things at a level I (as a relative beginner) can understand. For example, it goes into what resistors are and why they are important.
However, I do have a couple of nits to pick.
First, I was disappointed that there wasn't a more detailed explanation in some areas. I don't understand circuit diagrams (yet), but if you show me a picture of a Raspberry Pi and a breadboard, and what wire should go where, and where I should put the resistors and other components, I can follow that. Hopefully in the next edition of this book they will add more diagrams like this.
Second, the hardware project chapters were inconsistent. Some mentioned what components you needed to buy, others did not. A consistent table at the beginning or end of the chapter, including pictures of the component, would have been very helpful.
Finally, and most importantly. Be warned! This book is largely a selling vehicle for the PiFace component (in which the author(s) have a stake, if I'm not mistaken). That's a $45 component that you pretty much have to buy to follow this book. It's a great component, don't get me wrong, but spending more on the component than you did on the Raspberry Pi can be a bit of a shock.
The projects in this book could easily be done without the PiFace, but because the projects are PiFace-centered, you would have to translate not only the wiring, but also the code (as the PiFace has its own version of GPIO and its own Python libraries).
Great book, but be prepared to spend a pretty good sum of cash if you want to do the projects, and expect the occasional head scratch as you try to fill in the missing explanations.