Whether he's playing it geeky cool, sweet and sad or sly and dark, John Cusack almost always goes for characters who defy conventional boundaries, so the role of loving father might not seem a proper fit for the maverick leading man. But he wears it beautifully in "Martian Child,” a funny, poignant and ultimately uplifting study in the healing power of parental love.

Of course, Cusack's not playing the standard-iss...