It's messed up, yes. The sex isn't without purpose, but it's still a bunch of sex. I really enjoyed it, sex, violence, depth of human depravity and cruelty. All of it.
I think most who think it's trash don't like the bitter truth of what it means to be human. But I can understand why it's disliked, since you come to fantasy and stories like this to escape reality.
Good read, and like someone said before, it's horror disguised as hentai.