I don't really know how to review this thing, because I really disliked it. The story is just average for the anime of this kind (I mean hentai actually). It consists of constant blackmailing and sex scenes that follow, and I really wonder who would like it. In fact, the story could be described in a few words and it is just a small introduction to the sexual content. So let me say there is no actual story at all. I forced myself to watch it up to the end just to see what all this nonsense will finally lead to, and the ending disappointed me,too.
The characters also were of nothing special: one bad guy and a huge tribe of frightened innocent girls who later stop being innocent. I've seen many of that kind already.
The sound was ok, and the art reflected the atmosphere (was supposed to, at least), but imho was too dark.
To sum up, a mediocre product that can will most likely arouse the feeling of disgust, but not pleasure from watching.