Delirium

Normally I do not like horror movies built on the idea that the protagonist is mentally ill, and that one does not know if what he sees is real or only hallucinations as an effect of his illness (or alternatively a side effect of his medication). That concept has been overused in horror movies from this century.

But apart from that, I think this movie was really good. There were many good scares, many creepy discoveries, good acting and generally high production values.