This film has great action - well-choreographed, visceral, intense fight scenes that are as memorable as they are nasty - that's wrapped around an emotional core. The simplicity of the plot (dangerous man hunts down men who kidnapped a little girl) works so beautifully as a vehicle for the action scenes, but it also allows for the intense performances to shine through and take centre stage.
Won Bin steals the show as a broken man who seems to have shut in on himself in every way. When his little next door neighbour is kidnapped he goes on a rampage to bring her back. I believe him in every moment, as he reveals different facets of the character. I believed him as the taciturn, closed off pawn shop owner, as the lethal killer seeking revenge and justice, as the devastated husband losing his pregnant wife, and as the man we see at the end of the film: a man who has found some measure of peace and can now rest. His eyes are so expressive that he could carry a three minute close-up of just his face, and he makes the fight sequences so believable. A favourite scene is the one early on, when the two gangsters come to his apartment thinking he's just some chump next-door. He is so menacing that he barely has to move and you can feel the tension spike in the room. He has great physical presence.
The rest of the cast is very good, and the plot trucks along nicely. There is very little fat that gets in the way of the tale they are trying to tell. The fight scenes (for all the praise they get) are somewhat sparse, but in my opinion this only increases the tension in the film. For the first little while we actually rarely see our leading man actually fight. We see the very beginning and the aftermath, but never him in action. In my opinion, this makes his later fight scenes (in the club bathroom, the knife fight) even more memorable because they stand so on their own.
I want to make one final note about the cinematography of the film. In general I really enjoyed it, but I want to make special mention of the ending, particularly the scene where he realizes that the little girl isn't actually dead. The way it is shot and framed, and the lighting, is so dramatic and wonderful. The way the light catches his face and the way he looks up towards the sky -- it's like he's a man who is reckoning with God.
I think what sets this film apart from a lot of the other revenge action thrillers out there is the emotional intensity at the heart of the film. I BELIEVE in this man's singular love for this child, and I BELIEVE him when he says that he as nothing left to live for and nothing left to lose if she dies. He doesn't even care about going to jail afterward. It's about goodness existing in the world, and innocence, and him being able to protect the ones he cares about the way he couldn't before. Despite everything, there's something beautiful about the film. It feels as though we're witnessing someone's spiritual journey.