This is an excellent book for learning GWT, but it does assume some background knowledge in other topics, so it is not the simplest book.
I personally found that this book mentions and uses many design patterns, but if you have never studied design patterns (as a fair amount of computer scientists have not), then this book could be pretty difficult to follow.
However, if you do understand design patterns, then you will know what the author is talking about and realize that all of the sample programs and apps that are designed are truly designed well. The author shows how to use and combine great coding techniques and patterns to develop a strong application that is flexible and extensible.
Because of some of these assumptions, the textbook can be confusing, but if you do have the knowledge that is assumed, then this is an EXCELLENT textbook.
(For design patterns, I recommend the book Head First Design Patterns - it is an excellent book that covers the major design patterns and is quite enjoyable to read. You will learn all the patterns needed in that book to be able to follow GWT In Practice).
If you are looking to just make some simple apps in GWT but are not aiming for flexible, commercial level software, then you might want to look elsewhere for other textbooks. GWT In Action is much easier to follow, although it is a little dated now. However, it covers the basics of GWT which (at the time of this review) have not changed.