If all programming books were written this way, there would be a lot more competent programmers in the world. Not only is this book chock full of useful information about ActionScript and game programming, but the author continues in the vein of his first book (Foundation Game Design with Flash) by taking his time to explain thought processes and reasons for doing--or not doing--certain things. I am impressed by Rex Van der Spuy's attention to the smallest detail. He explains code by first examining a problem, describing its general solution, then delineating the specific implementation of that solution in code, line by line. Brilliantly done, and smoothly executed.
This is not, however, a book for beginners. No, this is definitely advanced; hence, the title. If you are not comfortable with class structures, design patterns and OOP concepts, or are unsure about how to write AS3 in general, I suggest you look elsewhere. Friends of Ed has some excellent titles that cater to all knowledge levels. Van der Spuy even refers to other titles/authors in his book; a non-self-serving aspect which I appreciate.
This is not light reading, either. Don't skim through expecting to find a quick solution to your specific problem. Start at the beginning, including the introduction because he explains how you should set up your work environment. Then go at your own pace through each chapter. The chapter sequence is logical and cumulative, the example files/code work correctly, there is plenty of side-note information, and the spelling and grammar are near perfect. I only found one error (p. 49 -- "drawn using with the drawing API"), which is amazing considering how many books get published with typos galore. (Note to editors: do a better job. Note to publishers: LET your editors do a better job.)
Topics I found to be particularly useful include: Verlet vs Euler integration, simple methods to reduce CPU load, physics modeling, blitting, pixel-perfect collisions, and pathfinding. Don't be misled into thinking that's all there is though. All 700+ pages are filled with important techniques that will keep your brain busy for months, if not longer.
The few areas I thought were weak included his explanation of Flash's Sound and SoundChannel classes, his tendency at times to over-explain things, and only a scant reference to memory leaks, which Flash is known for. These are minor complaints, though; the book is ultimately an outstanding addition to any developer's library.
If you are an intermediate to advanced programmer, it should be on your shelf.