I'm a hobbyist comic book artist and to me this is the best book on this subject.
I have a lot traditional books on anatomy (In my opinion best ones are made by Andrew Loomis but unfortunately those are hard to find) but there are only few ones that tackle really well how to pencil and ink anatomy in American comic book style.
Best parts of this book for me where "muscles in action" (where you see how different actions change the appearance of different muscles and how muscles move over underlying skeleton). Also "effects of light on the body" together with "surface rendering" (that sections really shows what kind of line should be drawn and where to get good looking muscle groups in different poses and lighting conditions).
When I compare this book with other "learn to draw comics" -books I think that there are few good generalist books of similar quality like
Drawing Dynamic Comics (Cutting Edge (Watson-Guptill Paperback)) (Cutting Edge (Watson-Guptill Paperback)) or
How to Draw Comics the "Marvel" Way. Those books give you good overall understanding about what steps there is to comic pages from start to finish but those are little bit lacking in details about how to illustrate specific parts of anatomy in variety of positions.
Then there are books that are excellent but bit different in style like
Action! Cartooning: 96 Pages of How-to Havoc! or
Cartoon Cool: How to Draw TV's Retro Style Characters. These are good to widen your skill set and build good foundation to more simplified style but don't obviously help with detailed style used in Marvel/DC/Image -comic books.
Btw. about the criticism in earlier review I can say that many books in Hart- series are well.. a bit lacking in quality vise in my opinion. This book is nothing like that. It could be even more polished on few small aspects but same thing can be said about almost all books. Also it can be said that this book don't work too well as your only book. It should be bought in addition with some foundation book that covers all the comic making process from a to z.
The fact that there is different artists used in this book doesn't matter to me at least. Actually I think it's a good thing to see a how same thing can be accomplished with little bit of a variation.
I highly recommend this book to any beginner or intermediate comic book artist interested in drawing anatomy American comic book style.