The movie is partially about the kid and partially about his mother. The aspect of the boy reflects the plasticity of children and their ability to be content with what they have. Stuck in a room the size of a storage shed for the entirety of his five years of life, the kid manages to find things to do, things to play with, and generally be contented.
The mother is a different story. She was a young adult when first introduced to the room, and she is not nearly as easy to please. Likewise, she will have a harder time coping with the outside world when re-introduced to it. Everyone she knows (except family) will likely have moved on and all but forgotten her. She has to deal with all the choices she made and the situation that she was in - and that will be a hard thing to do.
The movie reminds me of Boyhood with the way it concentrates on the lives and relationship between the boy and his mother, and it examines the intricacies and changes that happen due to stress and an ever-changing world. Unlike that movie, this one was of tolerable length and had enough intriguing sub-lots to keep my interest through the whole thing.
Acting was good
Direction was good
Story was very good
Pacing was slow, but just right
Cinematography was good
Bottom Line: A good movie. Not a great one, but solid.