First of all, a round of applause for KANG HA NEUL!
If a movie has to be good then actors must do a good job too only then a movie can be better, well you can say this is one of the reasons why this movie is good!
Another reason is the powerpack suspense of the movie, well if you have watched many movies then I can say you can guess in advance some points but not all, IT'S RECOMMENDED TO ALL SUSPENSE LOVERS!
EMOTIONAL TOUCH you can only feel when you are quite connected till the end, everyone was pitiable and everyone was quite scary.