I approached this book as one kind of newbie -- a web designer/programmer who is proficient at javascript and other scripting languages, but with little experience in After Effects. So, while I was comfortable with the scripting elements of the book, I appreciated the fact that various users of After Effects will arrive from any number of different backgrounds, and the effort taken to not scare off visual designers with lots of unfamiliar math and programming language were not a problem for me. Expressions is a clever pun of Adobe's in a way, using a word that we might take to mean "artistic expression" to fuel an approach to entering mathematical expressions, for underlying these dazzling effects is math. For those of us who are programmers, of course, the ability that Expressions gives to get to the actual math and javascript is a plus that increases our comfort level with our goals for the finished product.
This book does a good job of easing the burden of the math/programming for those who aren't at their most comfortable with these things, and does an equally good job of taking someone like myself, who is likely to be involved more in the programming side of a project while working with a designer, to become familiar with the parameters used by Expressions. This acknowledges, in my mind, that there are various of us in the food chain of producing content that may have to learn to touch a wide array of different programs (for instance, I had rarely used Adobe Premiere before last year, and it was one of my most-used programs in 2008 because of web projects that were heavy on video). That's why I think it is important for a book of this kind to be able to welcome various kinds of newbies... folks who may all be newbies in different ways.
I had no problem, by the way, using the sample files on a PC, so perhaps this problem was fixed since the time another reviewer reported problems.
Within just a few minutes, I was able to alter Expressions commands in After Effects, and, thanks to this book, had a sense of how the parameters I was altering were creating the changed results.
The format of this book was very easy to follow, and the illustrations were of superb quality. In a few cases, it made all the difference to know what I was looking for in the visual sense, by seeing the high-quality color rendering that the book provided.
This book really solves a problem for me, that I increasingly face in my responsibilities with content production problems, which is the need to get up to speed quickly and specifically on an application (or, in this case, a portion of an application) utilized in a project in which I work with others. I now have a much greater level of confidence in being able to dig in to After Effects, and use the power Expressions as an aid to creating the desired results.