Uzumaki

Masterpiece, only sold short by its abrupt ending.
There's so much to talk about in this particular omnibus (only the second horror manga I've ever read) - body horror, cannibalism, and so on - that you must read it to believe it. A small coastal town in Japan is cursed (hence the name, which means spiral in Japanese), and everything goes to hell. There are short stories on everything - such as mosquitoes (whose flying pattern is similar), snails (with the shape of their backs), and even tornadoes.
There's little to no characterization here, and I didn't know beforehand that this was a loose collection of short stories with a joining narrative, but that didn't detract from my immersion. There are the usual tropes here - a slightly unhinged deuteragonist with a gory past, the protagonist who's somehow not affected by the mania happening, and so on. Where Uzumaki shines is in creating a sense of helplessness - at no point do you feel that the characters are in control of what's happening, and this is different from the horror we're used to (the main character saving the day). I'd recommend this only for second-hand helplessness if nothing else.