Essential GWT is a misleading title. You could suppose, as I did, that it contains at least GWT basics. It doesn't. There is an overview of GWT, but nothing which will get you started if you're a beginner. So if you're expecting a tutorial about GWT development, widgets, etc..., pass your way. You should read another book or the online tutorial first. This book should have been named something like "Practical GWT Cookbook", as it contains some recipes about common web development topics like file uploading, security and much more.
I felt that the first half of the book was not very well structured. For example, I didn't understand why there is a paragraph on Code Generation in Chapter 4, Working with Browsers. Explanations are illustrated with code samples, but there are either too few, or too much. Too much, like the methods of the JDBC examples. Only one would have been enough. Too few, like the EJB example. Someone who knows EJB will know how to call a bean. Someone who doesn't will need much more information.
There are some annoying errors, especially in the MVP explanation. The same class gets three or four different names, making it very difficult to follow. MVP is an "essential" topic in this book, so it should have been carefully polished.
Nevertheless, the book still contains some interesting tips and techniques. I particularly enjoyed the speed measurement and the testing chapter. But overall I think it is falling short at explaining the essential.
