It's a modern classic. Those who hate it either misinterpreted the trailer and paid for a diffrent style of movie, or gave the excuse that the movie is slow withought taking into considiration that the sudden rapid progression of the movie's plot is part of the chaotic story format being told and such criticism are of those who enquire that a movie must be full of, jumpscares if you will, to uphold a temporary, bland, repetitive and predictable yet some what consistent approach rather than a unorthodox plot progression that has less that of jumpscares and relies primarily upon the fear of the unknown presented heavily after half of the runtime. I for one, would indeed rather have a memorable experience that is actually disturbing even if that is present after half of the movie's runtime being used to explain the storyline rather than a consistent boredom of jumpscares. Finally those who distaste the movie may also think as such due to the fact that the movie is rather confusing to a certain degree and is mostly new type/style of horror towards many of the viewers tastes especially if they misinterpreted the trailer and as such will be very well underprepared for such a heavy and diffrent style of plot that if to be placed in a analogical way, the plot presented is that similar of a riddle or a puzzle if so to speak. So in that i say this movie is underappreciated and is worth your time but note, it has an unorthodox approach and the climax is quite deep in the movies runtime. Secondly, note that the trailer is misleading, instead just consider this as a modern take on cult horror. Finally the plot is fairly confusing since it is rather an odd movies/story so be prepared to take note in ones mind of every little clue presented in the film as so throughout the movie's progression to provide a smooth understanding for one's viewing pleasure.
Personal opinion of the movie: 9/10