This started out well. A holiday scene in a beautiful location. My type of film. Something to carry me away from the concrete greyness of city life. Things turned darker as the film progressed. OK. I expected that in order to move the narrative along. But the final stretch was just perplexing. Histrionic and melodramatic, yes. But not quite sure if that makes it a 'horror' film (it's not a genre I'm that familiar with). What the story lacks - in spades - is a motive. We have no idea why the hosts act as they do. Perhaps they'd lived troubled lives which may have helped to explain their actions, but IF that was the case, it went unexplored.
I'd put this in the same category as Alex Garland's recent film 'Men', which also falls in the final act and, in so doing,makes you question everything you watched that preceded it. Disappointing - to say the least.