This is pitched as a dark thriller and a black comedy, and some of the extreme aspects of both are difficult to watch. It's not the sex and violence, because there isn't any on screen. It's the malign misogyny (and yes, the misanthropy) of the lead character which is hard to endure, though the audience's repulsion is factored in.
Luis Tosar is effectively creepy as a depressed/psychopathic concierge at a swanky apartment building who wants to make his residents as miserable as possible because he can't feel any pleasure himself. His biggest challenge is a fun/sexy/vulnerable señorita living alone, and to make her sad he has to really be bad.
Marta Etura plays the woman-in-peril and her sunny day élan is a release. But when the obsessive surveillance of the male oppressor grows into sexual assault then it goes too far for mere escapism. And the final twist offers no satisfaction. The story soon runs out of logic, though this is hardly unusual in a psychological thriller.
As a suspense picture, it is directed by Jaume Balagueró with some real flair; this is edgy stuff. For a while the comedy doesn't register, but the events are so absurd that eventually an unsettling comic resonance can be detected. Actually, if I was the sort who does, I might have pulled the plug; but maybe I'm easily offended...