- Adaptation Displacement: The manga has been all but dwarfed by the film.
- Awesome Music: The first movement of Vivaldi's "Four Seasons: Winter" certainly takes the cake, but the entire soundtrack of this movie is a work of genius. Every track is named after a famous movie classic (most of them film noir) yet every title also clearly applies to the events seen in the film when the track is played. Every major character has a theme that is played overtly in several scenes, rather than recurring only as background music. Lee Woo-Jin's theme is lovingly used throughout the film; it is also heard as the jingle marking the release of the gas in Dae-Su's prison and it is the ringtone on the phone given to him by Woo-Jin. The pieces themselves are so appropriate and original that even hearing a few seconds of any part of the soundtrack will instantly conjure up the atmosphere of the movie.
- Crosses the Line Twice: The tension and dark subject matter in the movie makes a lot of the Black Comedy stand out.
- After Dae-su reveals his tragic story to the man about to commit suicide, the man is stunned. As soon as he tries to tell his own story, Dae-su just stands up and walks away.
- Oh Dae-su and Mi-do receive a severed hand in the mail as an intimidation tactic. Oh Dae-su stares at it, recognizing who it's from and how it functions as an intimidation tactic, whereas Mi-do... unceremoniously faints.
- Esoteric Happy Ending: According to the director, it's either a happy ending that's sad or a sad ending that's happy. Either way, there's the possibility that the protagonist continues to carry on an incestuous relationship with his own unwitting daughter, and that he may or may not know himself.
- Funny Moments:
- When Oh Dae-Su walks away from the upset woman and the suicide guy falls on the car close by. The smile he gives clinches it.
- The dotted line from the hammer to the mook's head, complete with Mickey Mousing: "Tick tick tick tick DING!"
- Dae-su repeating the youth slang he's recently heard. "Why did you lock me up, you... Dickshit?"
- Moment of Awesome: The legendary hallway fight.
- Nightmare Fuel: Much of the movie, particularly the Gory Discretion Shot.
- Paranoia Fuel: Dae-su was locked up in an apartment for 15 years, and tricked into sleeping with his daughter all because he had inadvertently spread a rumor about a classmate in high school.
- Signature Scene: The hallway fight, to the point where many people unfamiliar with the film assume it to be an action movie based solely on this scene.
- Spiritual Adaptation: More than a few critics have called it a spiritual remake of Brian De Palma's Obsession, which was in turn, a spiritual remake of Vertigo. Both Obsession and Oldboy have a few things in common, particularly the twist ending.
- Squick: Played first for laughs (like the octopus scene), but getting steadily darker as the film goes on. Especially the ending.
- Tear Jerker:
- Several scenes, but especially the unbearable finale when Dae-su screams and grovels before Woo-Jin, begging him not to tell Mi-do that Dae-su is her father.
- "The Last Waltz", which plays during Mi-do's fantasy of the ant on the train and during the end credits, is a Tear Jerker all of itself, when the movie is over.
- The Woobie:
- Oh Dae-Su. The dude gets locked up alone in a hotel room for fifteen years straight without being told why, and then finds out that he's been manipulated into banging his own daughter.
- Mi-do, especially when it turns out that she is an Unwitting Pawn in the Big Bad's decades-long plan to punish her father for something he did in high school.
- Tragic Villain: Woo-jin is one of the best examples in cinema. Through the course of the movie he murders people, imprisons a man for 15 years, tortures him and tricks him into sleeping with his daughter, all for starting a rumor. But when the film flashes back to Woo-jin on the bridge, desperately holding on to his sister as she hangs over the water, you realize that he is ultimately a broken man who needed an excuse, no matter how flimsy, to go on as once he got his revenge he promptly committed suicide.
- Unintentionally Unsympathetic: While the tragic loss of his sister after trying desperately to save her is a horrible thing for Woo-jin to go through, it really doesn't justify the horrific things that he does to Dae-su in any way shape or form. Beyond the simple Aesop that revenge is bad, Dae-su had literally nothing to do with Soo-ah committing suicide and even the flimsy excuse that Dae-su spreading rumors was the cause if it loses water when you realize that anyone could have accidentally stumbled upon what Woo-jin and Soo-ah were doing at the school. Ultimately, Woo-jin was just a broken man who needed a reason to go on and while that is tragic, his desire for revenge towards Dae-su was petty, childish, and just a way to keep him from reflecting on his own part in Soo-ah's demise because if they hadn't been doing what they were doing in public then no one would have seen and his sister's reputation wouldn't have been destroyed thus driving her to suicide. To some extent, this is intentional, at least in regards to Woo-Jin's interpretation of his sister's pregnancy being a "phantom pregnancy", which only a deluded person in denial about the consequences of his twisted relationship could think up.
YMMV / Oldboy (2003)