Reading the reviews for this book made me nervous about picking it up in the first place, but I'm glad I did. I'm primarily a J2EE developer wanting to get his feet wet in the world of Flex2 RIAs, and the authors seem to have written this just for someone like me. And in that respect, the topics are at the right level of depth - the authors clearly indicate that this is not meant to be used as an API reference.
Flex 2 can be a bit much to bite off, even for experienced programmers, since it sits over a very mature and complex development platform (Flash Player) that has its own established authoring tool. Happily, the authors tend to chart their course firmly through the Flex Framework, avoiding diversions into Flash Player arcana (which some other books either assume you already know, or visit too briefly to be of much help.)
The breadth of topics covered is also awesome - whether its Web services, states/transitions, event dispatching/handling, and the use of the free Flex SDK.
That last one is of particular interest to me since I'm not a fan of the Deux Ex Machina aspects of IDEs, especially when I'm learning a new language/framework. Hence, being able to see how everything fits together using just the Flex SDK and mxmlc is a lot of fun.
I also don't particularly like long, artificial examples that proceed from chapter to chapter, which means that you can't really jump into a topic that interests you without first having read all the previous history of the application being developed. Fortunately here, each chapter can be read by itself, and in any order. In fact, I skipped over many of the UI and media chapters just to get to the web services treatment which is closer to the end.
To summarize - if your background/needs match mine, then this book will be well worth a visit. You may not leave knowing everything, but you'll have the 3000 foot overview which will position you better to ask the right questions, and to determine which topic has the most interest for you. (Of course, you might choose to wait for the Flex 3.0 edition of this book.)