The book isn't perfect. There is a little too much repetition of some facts and I have my doubts about this being the story of a seven year old boy, especially considering the many secrets he is expected to keep. But these problems are pretty easy to overlook.
The tale is inviting, with enough sub-plots to keep the reader interested. It gives a fine picture of 1952 farm life, and doesn't make even its most sympathetic characters too perfect (a la Hallmark). As the theme of the novel is secrecy, there is plenty of intrigue. But there is also a good deal of humor as well. The tone is engaging and smooth throughout.
Subtly, Grisham seems to be making statements about race and class distinctions. The novel's protagonist does come to all the right conclusions, even when his own motives are not so pure. The family must deal with two sets of workers: Mexicans and Hill People (whites who come from other parts of Arkansas to pick cotton). The differences are dealt with more in a matter-of-fact manner, particularly since the main character is more interested in baseball than the rights and concerns of people outside his family. So Grisham avoids hitting his reader over the head with moralizing.
I do recommend "A Painted House," but I won't likely see the movie anytime soon. I have my own prejudices getting in the way of that.