Differently from most part of tech books explaining libraries, tools and languages, I found this book quite complex. The author is a real expert of Java web applications, and tries to put all his expertise not only of Tapestry, but of Web application development, all throughout the book. Every chapter starts with a rather simple example, but develops rapidly showing different aspects and example of real applications.
If you want to learn all about Tapestry, this is the right book for you. You will learn how to develop simple and complex web applications, how to build reusable components, but you will also understand the internals of the framework. All in a book.
Conversely, if your goal is only to have an overview of the framework, be prepared to face an high-detailed and complex book, and dive through the secrets and the difficulties of writing a modern MVC framework. Definitely, it is not a "for dummies" book.