The writing style isn't particularly sophisticated and tends to repeat itself. It also makes many assumptions and draws on very few scientific sources of information. Its heart is in the right place, but its not all too convincing. The basic claim that we are apes and should behave and move as such is romantic, but it doesn't account for the fact that we are evolved, therefore different, from apes (granted we share many similarities).
As an example, he claims that ultra-endurance athletes aren't natural because they are mimicking migratory birds, rather than apes, and attributes the claim to the number of injuries that the sports accure. He doesn't take into account that it may be what those endurance athletes are using (improper running form) to account for those injuries, especially when there is evidence of human pockets that routinely travel hundreds of miles for fun (Mexico, Japan, etc) and rarely suffer related injuries. It also doesn't account for observed persistance hunting practices where running long distances with tracking skill were required for meat acquisition in some African tribes, some would call the cradle of evolution. Apes have underdeveloped gluteal muscles and weren't adapted for running and lack a nuchal ligament, a ligament that enables cats and humans to maintain head position when running. Humans have a well developed glutes for locomotion and have a nuchal ligament, providing evidence that sometime during our evolutionary development, running was selected for (otherwise no one would have it). If the author dismissed running so handedly, I would take the rest of the book with a critical eye.
Granted, I am no expert in anthropology or physiology, I would imagine someone to write a relatively recent book on human movement to take such things into account. The complete omittance of evidence, especially evidence that would allow people another venue of physical activity, is surprising and depressing. But if the book gets people off the couch and moving again, I can't complain.