I've been playing with Struts ever since 1.0 came out. However, I haven't worked with Struts on anything more than simple applications, which made this book sound like a perfect match for my needs. Especially as it covers Struts 1.2 (beta).
Mister Holzner does a great job explaining certain things that many other resources seem to omit, assuming that the reader can figure it out on her own (often by reading source code). In general, the book's contents feels like a good match for the book's stated target audience.
The negative remarks I wrote down while going through the chapters included a lot of tiny issues like not explaining all attributes (even with a one-sentence mention) of the action mappings in a Struts configuration file. Also, it was weird to be taught how one uses "javac" -- the book clearly states that working knowledge of Java is assumed.
Furthermore, many example code snippets in the book use horrible package and class names such as "ch03.ch03_05", which makes it unnecessarily difficult to keep track of which file is which. Also, the decision to employ a custom taglib, <ch03:toppings/>, just to set up a list of items for testing when a simple scriptlet would do?
Regardless of me whining about the smaller issues, I'd say "Struts: Essential Skills" is a great learning resource for Struts. It's far from sufficient as a reference, but I've never seen as effective a Struts tutorial than this.