It is the story of a young man from the picturesque Haute Savoie region of southern France who passes himself off as a ghetto rocker/rapper, and builds a huge career as a flashy rapper. It's all fake, though, and that's what this movie is about: the superficiality of manufactured successes in modern pop music.
At one point, when Fatal's real story is exposed, there is a moment of truth telling: Fatal and his rival express their real feelings to their public. This could easily have become a made-for-TV mess at this point. But it doesn't, because it realizes that audiences don't really want sincerity, they just want the latest manufactured hype.
Not a great movie, certainly, but a very entertaining one with some intelligent ideas well worked out. An American version of this could be very entertaining as well, but I find it hard to believe an American producer would allow it to be this cynical about the nature of modern music audiences.