Darren Carver-Balsiger’s review published on Letterboxd:
Hammer to the face. Before Parasite was the Korean film adored by the West, there was Oldboy. Nothing can prepare someone for their first viewing of Oldboy. For those who ever revisit it, they forget how darkly comic so much of it seemed at first. It's as if the memory is erased.
Oldboy is a nightmare. Not only because it is so deeply disturbing, but because its black void of evil is so insidious we relate to pain we cannot have gone through. When Oh Dae-su begs by the end, truly the most pathetic of sights, the nightmare is that you understand why. Oldboy has layers of revenge, vengeance pointed in opposite directions, but what's hard to pin is why. The revenge isn't pointless, it is in fact argued for, and yet its great swathe of pain cannot be seen as righteous. The revenge is too petty, too minor to justify its overreach. That is why it's a nightmare.
Oldboy is a masterpiece. It has a perfect finale which rides the many waves of twists and turns that come before. It is also of its time. This is peak early-2000s aesthetic. It is executed with ideas beyond its scope, stylised in a brilliantly vulgar arthouse manner. The physicality of performance and power of suggestion makes this a lot less explicitly violent then you remember. But that matches the point. Experiences change you.
There's only misery here, not even cold joy enters the world of Oldboy. Yet its pain slumps your soul and gets the heart racing. And there's always the big uncertainty: what does the final, pained smile mean?