I watched this movie on a whim without knowing anything about it beforehand, and I was pleasantly surprised at how gory, disturbing and downright entertaining the movie ended up being. The film follows a similar set up to many of the recent Japanese/Korean high school films; Students are locked in a school and picked off one by one by an unseen force. This time, however, the force is asking the brightest and most intelligent students to solve questions in order to save the lives of their peers. It's a great set-up that flows nicely between each act, with some great practical effects and some disturbing and downright horrifying scenes involving the teens. The acting was great all around, save for a few of the students that seemed to not have much experience or didn't take their roles too seriously. And while the movie seemed to get a bit confusing towards the final act, it all came together nicely in a twist that was not only unexpected, but very well executed. My only gripe with this film was that it could have been a bit more graphic with its depiction of death. I wanted to see each person as they were being killed, if only to increase the tension and disturbing element of an already pretty effective set-up. Overall, one of the better South Korean horror films I have seen, and definitely recommended for anyone who enjoys seeing annoying High School kids get their just deserts. A success, as far as I'm concerned.
