I think that this book is a good book.
There's nothing in it that over-challenges those with a reasonable memory of "high-school" mathematics, and a smattering of knowledge of what computers do. However, education is not its purpose.
The approach taken by the author is clever, relaxed, and is sufficiently different to traditional teaching (of both mathematics and computing) to warrant maintained interest. The embedding of historical notes (biographical and anecdotal) in book is very good, again sustaining the reader's attention.
I will recommend this book to my son when he's about 15 years old, to give him an appreciation of the depth of importance and ingenuity that is our mathematical heritage.
I'm tempted to give this book the five-star treatment. It doesn't get five-stars, because I believe it could go into greater depth without losing its integrity. However, maybe that is its greatest strength - that it covers a variety of subjects in sufficient detail, without switching the reader off...