The movie itself is excellent. It points out the problems in our modern diets, and gives a method of being healthy that has been nothing short of a miracle for me and my family.
To address some issues others have had:
It is true that life was hard during earlier times, meaning that only those that could survive in such harsh conditions could survive. This shaped us, but says nothing of our lifestyles today. If anything, this could help explain why intermittent fasting is so beneficial.
Many insects/bugs are anything but unhealthy. You can think they're disgusting as an effect of the culture of your upbringing, sure, but to claim they're all unhealthy is just untrue.
You can't conflate diet with hygiene. I don't counter vegetarians with "if all you want to do is eat plants in small meals, why don't you just take off all your clothes, ruminate, and forget about toilets?"
If you don't think hunting, gathering, walking everywhere, crafting, and everything else that comes along with living as our ancestors did constitutes exercise, I can't imagine what would. Take a look at the physical fitness of modern H/G tribes and tell me they don't exercise.
Humans are the most versatile species ever. We live and have lived everywhere from below sea level to the tops of mountains, from desert to jungle, eating every plant or animal that didn't kill us. To claim that a majority of humans throughout our evolution were primarily fishers is nonsense. At the very least, humans have been hunting for two _million_ years. More than enough to help shape us.
Look at native populations all over the world. The Anbarra, Arnhem, Ache, Nukak, Hiwi, !Kung, and Hazda tribes. All eating the historical diets of their people, and all in good enough shape to live many long years in incredibly difficult environments.
"Many long years?", you say? "But I thought they only lived to 40!" You might want to read the paper "Longevity Among Hunter-Gatherers: A Cross- Cultural Examination." Hunter/Gatherers live to be 80. Want to know something even better? Many H/Gs get 70-80% of their calories from meat, and they have no atherosclerosis (per other papers by Kaplan, et al.).
As for grains, while the heritage strains of wheat that we have been farming for the last 10k years might be fine, the fact is that the wheat we eat today is nothing even close. It should be considered an entirely new food type. Not to say that humans haven't found a new food and thrived on it before, of course, just that pointing out how long we've been eating it is irrelevant when it's been completely overhauled.
In summary, the movie does an excellent job pointing out the problems of a modern diet, and offers an alternative that has proved to be hugely beneficial to those that try it. Humans function best when we eat what humans have eaten throughout our entire evolution: real food. Given our long evolutionary history of eating everything with a pulse, that should definitely include animals--meat, offal, marrow and all.
