Yes it is. I was surprised at the sincere effort and success of a Hollywood production portraying a part of the population that is typically only mocked, if recognized at all.
Duvall was brilliant. The movie just had no weaknesses at all.
He wrote it, and has acted in or written several other wonderful movies with deeply, quietly Christian themes of individuals struggling with sin. The Great Santini, Tender Mercies, A Family Thing, Secondhand Lions, Open Range and Get Low spring to mind.