Oh, well, that's a weird manga.
I know it doesn't explain anything at all and lacks totally of common sense, but I liked it some way. I think if the author try to explain, would just mess up even more, you know? Because nothing makes sense, like, snail people, c'mon! But is creepy and interesting in a really weird way.
I don't think I wasted my time reading, has some good stories, if you analyse it one by one. The end is not terrible too, I totally wanted Kirie and Suichi out of the town (they survived until now, they could make it somehow...), but I liked both died together (that hug was the best part, wish it was a full-page image).
So, I will give 8/10, because it made me laugh and feel disgusted at the same time, has a incredible art (man, those spirals are cool) and it made me dream with cannibal schoolmates when I read it before going to sleep.