Business is slow at first, but picks up, along with the body count. A suicide gets the ball rolling and it gathers speed thanks largely to a combination of ill-fortune and incompetence, topped off by the curse of an old hag.
This film was apparently the base material for The Happiness of the Katakuris, which I have yet to watch. Takeshi Miike apparently added zombies and singing, which sounds a bit like over-seasoning to me.
Ji-woon Kim later directed one of my favourite films of the past decade — A Tale of Two Sisters — from this evidence, not a one-off.