There are few "based on a true story" films out there that make me cringe, but this just happens to be one of them.
For details on the actual case: Gertrude Baniszewski Case
Given the background on the story, it's hard to imagine translating this sort of true inhumanity onto the silver screen. However, director Tommy O'Haver teamed with co-writer Irene Turner managed to weave together a horrifically realistic portrayal of the events.
The victim Sylvia Likens is played by young actress Ellen Page (of Juno fame), and she does an incredible job portraying a viciously abused and confused child. I first saw her in Hard Candy and I'm amazed at her range considering her youthfulness.
In fact, all of the main characters had that gritty realism that really made this film work.
The film is careful not too go strong on the graphic visuals, but the various abuse scenes are done so well that you get far more out of it by not seeing exactly what is going on. (This is especially true for one particular scene that would have merited an X rating had they shown everything.)
I'm hard-pressed to pinpoint anything I didn't like about the film, which is unusual for me. It's definitely not a date movie, and it does tug at a mixture of unpleasant emotions while viewing. At times it seems almost unbelievable until you look up the actual case and realize that they probably held quite a bit back.
Info on IMDB: An American Crime