The terror comes not from vast amount of gore or violence on the screen - because there's almost none. There's violence, but it's all behind the frame, we never see even a single disfigured human body. The terror comes from a pure concepts that this anime explores.
Story:
It's a thriller, it grips you and tightens it's hands around you. You feel horrible, but keep watching and it only lets go at the very end. It's been a long time since I've seen such a good crafted story, with the right hints planted for you to figure out things before they unfold before you, yet with mysteries so clever, that there's a very small of you succeeding.
Art:
I would understand if someone doesn't likes it. It's not "unique" it's just that they used flat colors for everything. No shading, no gradient. And I liked it. It looks surrealistic, but it doesn't throw you off at first like Katanagatari or Kaiba did.
Sound:
The tunes kick in the right time and deliver the right kind of emotional push for the given situations. Enhances the story in every way.
Character:
It's always hard for me with characters, usually I end up hating them for doing something obviously stupid and not seeing the situation clearly, or by being too perfect, or some other reason. It's rare that I find characters appealing for what they are in the story, rather for what they are. Characters felt good, I don't know what I can add without spoilers.
Enjoyment:
Enjoyment... There was a lot of it, but at the same time - there was none. I felt terrible. The terror of what's going to happen, the pain in the chest from the sorrow after realising what actually happened. I couldn't say I enjoyed watching it. I definitely liked it, but it was not enjoyment that I felt in the process.
Overall it was the best "horror" anime I've ever watched. This was a pure terror. And although it already says "Rating: R - 17+ (violence & profanity)", I want to clear up something. There's little to nothing violence on the screen. You never see more than a blood. There is some violence to animals, but very little. And neither is there profanity in any way.
Yet this anime is not for children. It's too dark and terrifying for them. And for people who don't like seeing gore - don't worry, you're not going to, it's there, but not on the screen.
