Choi Min-sik performance here starts very important with the beginning of Oh Dae-su in a police station shortly before he will be kidnapped. Dae-su is a drunk in the station being loud until taken out by his friend. This is an important scene as Choi is portraying Dae-su as a bit of a mess. He certainly resembles little of how we will see him later on as Choi portrays him as really just a loud drunk who frankly is obnoxious. This is actually a very important moment as it shows the man Dae-su is at the beginning who is just a pretty lowly man to say the least.
Dae-su than suddenly disappears and finds him a room that is apparently a prison that he cannot escape from. At first Choi shows that the annoying drunk Dae-su to just a very scared man who freaks out due to having no idea why he in this place. Choi in a fairly broad way, but in an effective fashion that certainly fits the mood of the film, after all he does have ants crawling all over him in one scene, showing Dae-su devolve into a form of insanity. He handles it well showing it as a painful intensity that is mostly found in his disbelief of what has happened to him, despite not knowing why in the slightest.
Choi tones down though as he the time goes on and on in his cell. Choi changes to this moment and brings about a transformation in Oh Dae-su to a man with a purpose rather than what seemed to be an aimless man beforehand. Choi makes Dae-su still a crazed man, yet he seems to make it far more self contained, and infused into his driving factor which is his lust for revenge. He is good in portraying that really his want to learn who has done this to him is really what has become the primary facet of the man.
When Dae-su is released for reasons that are just as mysterious as why he was put in the prison to begin with, he goes out seeking who did this to him. Dae-su is a completely different man as Choi interestingly plays him as the opposite of the loud mouth at the beginning, which he earned through his transformation in the cell. Dae-su know has become a fairly quiet man, who rather blabbing all the time, seems rather stoic and reserved above all else. His insanity still remains but it comes out at specific times in a sharp distinct manner.
For example the octopus eating scene is of course a deranged scene as he shoves it down his throat, but Choi here effectively shows how Dae-su is now very much a man with a mission as strange and insane as the act is he does it in a controlled and almost stoic manner. Choi is actually quite outstanding in being able to bring to life the oxymoron of this character. It never seems unbelievable, and it always fits well within the style of this unique film.
Choi makes Dae-su quite the intriguing hero to follow through the mystery of the film. Choi does not make Dae-su to be any sort of brilliant detective or tactician, but what really pushes him forward is only his passion to find out the truth. Choi never loses a certain intensity as Dae-su searches for his captors that only grows as he approaches them. He properly brutal when he finally does meet some of them particularly with his free use of hammer. Of course the hammer does a lot of the work, but Choi perfectly conveys the violence Dae-su is capable of.
Dae-su though does not keep his composure forever though as Choi's most difficult scenes really come in at the end of the film when all is revealed to him, which leads him from one intense emotional moment to another. Choi is always very physical in this performance, throwing himself head first in every scene, and this especially true for the climax of the film. This certainly fits for the moments in the film for the revelations are not exactly one's that should be taken lightly, and reacting believably to these revelations is essential to the film, and Choi manages to pull it off.
The first revelation is that that Choi has been set up to commit one the worst sins, and Choibring the the pain, the anger, and the all around horror to the moment that sends Dae-su to the rage. He appropriately shows that Dae-su's is truly horrified by the revelation to the very core of his being. Quickly though after really being told of another revelation there Dae-su becomes filled with regret and remorse. Choi manages to actually bring this change about powerfully so in another scene where he dives right into insanity, and Choi shows that Dae-su loses all of his stoic qualities from before turning essentially into a broken man.
This is certainly a no bars held performance that is striking in just how many risks it takes, and how well they all pay off. Every moment of madness never seems overwrought or needless he makes them all part of the strange journey of Dae-su that becomes something both very powerful, and quite disturbing. Choi never stops for a moment in this bizarre but compelling characterization. It is never a straight forward or simple approach to this character utilizing a technique that very few actors would likely take. With his most unorthodox portrayal Choi makes Oh Dae-su a truly memorable protagonist.