It's a silly, dumb laugh. It's impossible to get annoyed with the daft characterisation and misuse of Japanese legend, because you're not meant to be taking anything here seriously. It's the kind of film where you're meant to laugh (and I did) at the bad special effects when someone's arm gets pulled off. (Those two delicate little blood spurts are comedy.)
The ending's surprisingly good, though.
To be honest, I think the film's better than it might have been. Look at the cast, for instance. The four main girls don't have that much acting experience. Its main star, Megumi Ohori, is a pin-up model, singer and TV personality who's since mostly retired from show business. Here, though, they're fine. They don't have much range (e.g. one girl's laughable reaction to losing some of her fingers), but that's not a problem since they're mostly just being asked to play themselves. They're lively and fun.
The first twenty minutes or so are just the girls on a hiking holiday. They've found a village with a festival and a "living god". (It's also so deep in the mountains that there's no phone signal.) The locals seem friendly, but words like "ritual sacrifice" can be heard in their conversations and every so often the film will hit us with horror movie music. This opening act feels like a normal movie. The situation feels real and the girls are likeable.
Then, though, the kuchisake-onna hits the screen and the film gets silly. If this were a serious film, I'd hate this kuchisake-onna design. She's not a human who's had her mouth cut open. She's a goofy alien tooth monster and occasionally you can also see the real teeth of the actress behind the mask. She also has one of my pet hates, i.e. an unnatural monster voice for her trademark phrase. That doesn't matter, though. She's a goofy monster in some cheap, fun trash. She's also bitey. (For what it's worth, the film's mythology is that she's some kind of mutant that's been being reborn in this village for centuries. They're the source of the kuchisake-onna legend, not the other way around. That's a satisfactory explanation, actually.)
The villagers are inbred. Look at the comedy idiots and tell me I'm wrong. That said, though, they're also evil enough that you'll be keenly anticipating their deaths in a kuchisake-pocalypse. (Their ritual had been going to be held in front of everyone, for instance.)
The ending, though, mildly impressed me. They do the inevitable horror twist ending. Of course. Obviously. You'd have fallen off your chair if they hadn't. After that, though, they do another one and then keep going. The film's last shot finds some emotional weight.
Is this a good film? No, but that's the wrong question. It's successful at doing what its makers wanted. It achieves its artistic goals. They're fairly silly, admittedly, but the film's doing its job of being lowbrow entertainment. It's also nowhere near as trashy as it could have been. There's no nudity, for instance. Obviously this isn't a film you need to watch, unless you're looking for hillbilly retard comedy, overdone gore effects and problematic story logic. (Why does that bloke think killing the current kuchisake-onna will end the rebirth cycle, since they keep being born to ordinary human women? Towards the end, when asked, how does SPOILER know that SPOILER and SPOILER are dead? Slightly disturbing suggestion: maybe she doesn't!)
Yet another kuchisake-onna film that's completely different from all the others I've seen. It's not a franchise. It's more interesting than that.