I was absolutely blown away, in the best possible way, by this movie. Gripping, chillingly plausible, the most terrifying and haunting horror film Iโve ever seen. It starts off being very creepy and unsettling and nothing prepares you for the unmitigated horror that it ever so gradually leads you into... A gasp-provoking twist towards the end is the turning point, so cleverly done. Do not watch it immediately before sleep, though - I had a nightmare as terrifying as the movie itself!
Also, as well as being brilliantly tense and frightening, it has an important theme and moral message: do not ignore, for the sake of politeness or obeying social niceties, a gut feeling of something not being right.