Martian Child: 5 out of 10.
I try to choose the movies I watch carefully. I read reviews and get feedback from people I trust before giving a film two hours of my life. The exception to this rule is kids movies I watch with my offspring, and, the odd time, I watch a movie because it stars an actor I like.
That last reason explains how I came to watch Martian Child. It stars John Cusack, an actor I usually like. In this film, he wasn't enough to keep me interested. It's all been done before, and in far more interesting fashion. Sure the kid is sweet and sure Cusack's belief in the boy pays dividends but Martian Child is so predictable by the time you get to the climax you feel as if you've been there a thousand times before.
Watch High Fidelity again instead.