The story is pretty original (not mindblowing, but original), and the screenplay is very well written. It revolves around a young boy and his father, whose occupation seems to be a bit of a mystery. The story is a mystery at first while you try to figure that out, and then it becomes a bittersweet drama for about the second half of the film. Unfortunately there's not much more I can say without spoiling it.
Robert Carlyle and Aaron Fuller (the young boy) were both brilliant. The performances are the real reason to watch this movie. I don't know where they found young Fuller, but for a newcomer he has substantial acting skills.
A little warning: The dialog in this movie is heavily British, and was not made with the American mainstream in mind. As an American I found it a bit hard to understand at times.