No Mercy is as Intense revenge thriller, that certainly lives up to it's name. The story is well told from start to finish. The ending is unexpected, but doesn't feel gimmicky like some twist endings I've seen. As revenge thrillers go, this one is near perfect. The story itself has a lot of familiar thriller elements. There's a murder mystery, a kidnapping, a race against time, and a cunning criminal behind it all. Ryoo Seung Bum is great as the subtle, and unsuspecting, mastermind Lee Seong Hyo. I liked that he wasn't a crazy over the top villain. It made him seem more sinister. He is matched against forensic expert Kang played by Sol Kyung Gu, and tenacious rookie detective Min Seo-yeong played by Han Hye Jin. Sol Kyung Gu was great, but I was a little less impressed with Min Seo-yeong. There was nothing wrong with how she played the character, but she just seemed a little timid and forgettable for my taste. There was also an obnoxious cop, who seemed too much like comic relief to me. Still, the entire cast was pretty solid, although the real star of this movie is the script. In the beginning the plot is pretty slow, but trust me when I say that you'll want to pay attention to all that's going on. I was reminded of other thrillers that I love (Silence of the Lambs, Se7en, Primal Fear) but I think No Mercy is still an original. I had no idea how it would all end until the very end. Now that I know the whole story, I am curious to watch it again from that perspective, but I admit that some of the suspense will be gone. I also want to warn viewers that there are some very graphic moments, but nothing explicit without a reason. I know it gets compared to Old Boy a lot, even by the friend who recommended it to me, but unlike Old Boy's over the top revenge ending, this ending was just brutally haunting. I think this is a must see for any fan of revenge thrillers, or if you just want to be told a great story (even if it's not a happy one).