Oldboy (2003)

No, not the US remake - this is the original South Korean Oldboy.
And boy is it good.
I first heard about Oldboy on The Film Podcast, and the way they raved about it made it a must see.
I'm glad to say they were Bang. On. The. Money... In a big way.
This movie is excellent.
It's one of the best "you screwed my life over, now I'm going to find and kill you" revenge movies I've ever seen.
Min-sik Choi stars as Dae-su Oh, who is kidnapped at the start of the film and imprisoned for 15 years for apparently no reason. While imprisoned, he finds out his daughter has been killed and somehow he is the prime suspect.
Fifteen years to the day since his kidnapping, Dae-su Oh is released from captivity, and driven by revenge, embarks on a mission of finding out who did this to him and why. And after spending much of those 15 years training himself to fight, you know he's going to kick some serious arse on the outside.
I'm not going any further into the plot because it's a film you have to see.
The Film Podcast crew hit the nail on the head regarding at least two memorable scenes.
The first: Dae-su Oh going into a restaurant and asking to eat something alive. The chef, Mi-do (Hye-jeong Kang), whacks an octopus in front of him and he promptly, you know, eats it. I don't know if it was seeing the octopus moving, the fact I had just served myself fish and chips or a combination of the two, but I could've been physically ill for quite a while afterwards.
The other scene is the hammer fight scene. The long take sees Dae-su Oh, armed only with a hammer and his awesome fighting skills, take on a whole bunch of bad guys in a corridor. And it is awesome.
Stick around as the twist at the end of the film is worth waiting around for (it took me by surprise though it probably shouldn't have), and you will be rewarded with having seen one of the best revenge/action films in world cinema.