I thought there were pros and cons to the movie.
We homeschool our kids, and we follow a "radical unschooling" philosophy. (I mention that as background)
I thought the movie presented a family who was living a very extreme lifestyle, which is fine, many of us here are considered extreme! but my main issue was the isolation of the kids, the lack of social peers, and lack of personal choice in their own lives. Obviously, one of the parents was seriously mentally ill, and there were some secretive behaviors happening (not wanting to give spoilers). But the kids seemed to have no outside friends or much contact with the outside world.
The end of the movie (SPOILER) goes too far in the opposite direction. There is a middle ground! My kids do not go to school, but we are a part of a large community of other homeschoolers, not to mention, friends, family, neighborhood. My kids take classes, participate in social events, and have access to many resources. My kids have an enormous say in their own activities.
I liked the performances, I thought the conflict between the family and the mom's family was interesting and sometimes funny, and sometimes really really sad. And, hey, I got to see naked Viggo Mortenson, full frontal! Nice!