Let's get this out of the way first - "Incredible Comic Book Women" is not the only book you'll ever need in order to draw comic book women well. No single such book exists.
Okay, now that we've cleared the air, "Incredible Comic Book Women" is probably the best book out there specifically dealing with how to draw the women of comics. Christopher Hart has written a book on the subject (How to Draw Great-Looking Comic Book Women (Christopher Hart Titles)) and other books (like How to Draw Fantasy Females: Create Sexy Cyberpunks, Seductive Supergirls, and Raunchy All-Action Heroines, Draw & Paint Fantasy Females, and How to Draw Those Bodacious Bad Babes of Comics) all have their good (and, unfortunately, mostly bad) points, but ICBW (as I'll refer to this book from here on in) is unique in that it takes its time in trying not only to teach you some of the basic and intermediate techniques, but it also has some great bits helping burgeoning artists recognize what they might be doing wrong, which is very important.
The book has 3 parts, each divided up into a series of segments:
Part 1: Drawing Crash Course tries to be a basic drawing fundamentals tutorial, covering gesture, face, hair, body structure, etc. The most helpful areas here are the "Gesture Sketches" and "Hair" sections - they teach some aspects of those difficult subjects that actually helped light bulbs go off in my head. The rest of this section offers similar content to Andy Smith's excellent DRAWING DYNAMIC COMICS, though, of course, this book focuses on women. The anatomy section in ICBW, however, are super helpful in that Nguyen's examples are drawn in positions and angles that will be most helpful to the artist - he actually draws the difficult 3/4 views of figures, which many books don't cover well or omit altogether. His discussions of the figure and body parts in perspective is not technical and I think will help greatly.
Part 2: Advanced Techniques offers discussion on using models as reference, drawing facial likenesses, drawing differing ethnicities, aging characters, clothing and accessories, and inking/coloring. Most of the lessons here are superficial, though the section of drawing a likeness is a good supplement to the excellent Secrets to Drawing Heads, which is highly recommended.
Part 3: Assignments shows him take a drawing of a comic book style woman from the conceptual stage all the way to the finish. These are well done, largely, and good for those trying to figure out the process of drawing. Especially helpful is one section which discusses how to draw clothing that had shiny areas on it, something very common in comics today. I've only ever seen on other book (Draw & Paint Fantasy Females) cover this topic at any length, but it can't touch Nguyen's analysis here, which will really make it seem easy.
The Good: In addition to a number of needed tutorials and examples, Nguyen, following in the footsteps of his last book, Incredible Comics with Tom Nguyen: The Ultimate Guide to Creating Kick-Ass Comic Art, shows us what not to do, often imitating the styles (and mistakes) of familiar comics professionals (who he doesn't identify by name. Season comics readers will get the joke, though...) in order to make his point. I tend to find these eye-opening, and they often point out what I've been doing wrong and couldn't figure out.
The Bad: Some parts of this book just don't work as well, or were done better in other books. While this book is certainly worth getting if you've got some experience under your belt, it's not good for the beginner. Additionally, judging by some of the content in this book, I would say it is meant for older artists, not for kids.