I have actually read this manga; it should be three volumes long. There is something about its simple and bizarre concept that's scary on a level not comparable to any other horror story I've read/watched. I vaguely remember some panels and storylines, even though I'd rather not remember them at all for just how creepy they look.
I've heard that the second episode has artwork and animation that don't live up to the high standard set by the first episode, but that the animators still wanted to publish it even when faced with many difficulties (the budget, cost cutting for example).