It was a very good movie, definitely one of the top korean horror/thriller movies I have ever seen. To really understand the depth of the story you need to pay close attention to the conversations and what is going on, because its not just a ghost/monster movie, its deeper than that. I think the people that say this was a waste of time did not really give the plot enough attention. It is not a jump-scare horror, its the kind that makes you feel heavy through out and leavs a dark feeling inside you afterwards.
10/10 recommend!