I rather liked this book. It is essentially an introductory work that uses simple Java programs to illustrate the principles and application of design patterns. The writing style is clear and seems to get to the point without waffle. It also has the advantage of covering all 23 of the GoF design patterns, although some of these, like Interpreter, are not often needed in practice. But it's good to have them all referenced in a single work, and the examples all seem to make sense on first reading. Another thing I've not seen in other works is that all of the pattern examples revolve around one common theme, that of a car manufacturer, so you can more easily see how different patterns are used for different purposes. This is certainly an improvement on the original GoF examples.
There is also a nice worked example for the MVC pattern, which is very useful considering most applications have a GUI somewhere and seeing how some of the other patterns interrelate to achieve MVC is quite instructive.
Simple UML diagrams supplemented by an appendix for those unfamiliar, though they are easy to pick up. There is also an appendix with a handy 'pattern on a page' summary which is very useful as a brief reminder.
You need to know the basics of Java as the book assumes some knowledge of how to code and basic OOP concepts. The code examples makes use of up to date Java features such as enums and the for-each construct, and the source code can be downloaded from the book's website.
There are a couple of minor typographical errors, though they don't really detract, and there's no mention of patterns for EJBs for example. But if you're new to the subject or been left confused by other explanations then this might just give you what you need to get started. It's not the longest book on the subject, though I guess this is reflected in the price.
Overall, a good introduction to the subject and a good price. Recommended.