Please excuse me for writing in English, I cannot write French that good anymore. The movie had been described as "ultra-hard", however I don't think the movie is that "hard" at all. However, please let me beginn:
The first half of the movie is of questionable quality. The introduction with the black/white part, well, maybe. But what follows, the killing of the family, the "monsters", this all leaves a bad taste in my mouth. This is like "hey, look, I'm an artist, look at me!" These episodes might be done better, certainly!
After the killing of the female victim from the hidden basement, the movie improves considerably. There's a storyline, a track has to be followed, and it works! A martyr has to be made, and we understand why and for what. This part is almost excellent, although I doubt if anyone would ever reach a stage to almost willingly let their skin peel off, with that sort of tender beating. The ending is superb, a sort of grim humour ending.
What bugs me, anyhow, is that I bought a French movie with just English subtitles. However... o.k. forget that.