and it doesn't shy away from the fact that their target audience is middle-aged men.

Man gets kidnapped and is locked up for 15 years (by the way, he looks the same age before and after) and becomes a badass, pro at fighting and spouting random facts (due to television being the only entertainment he had). Not only that, he gets a young girl as a lover (rather tragic, truly).

Conceptually I can give the story, acting, cinematography, and music great scores, yet this movie was hilarious and I couldn't take it seriously.

At the start it was funny and I chuckled at the nonsensical nature of it (if you like Japanese humor you will like it too). But then the second act starts and the viewer is supposed to care about... Characters.

Then climax and reveal happens, impressive acting performance, emotions going through the roof.
Yet I don't care. I don't even shed a tear or gasp in surprise (spoiler was revealed ages ago to me).

"Laugh and the world laughs with you. Weep, and you weep alone." wonderful quote that says how I feel about this movie.

One of the most annoying features of Oldboy- male gaze (our character is lustful). And at times it's quite random, especially in the second half (because in the first half it was played for comedic effect).

By the way, female characters here are basically just decoration (it's not about them after all + it's 2003 movie).

Will I rewatch this movie? Nah. If I need I will look up gifs or screencaps for wonderful cinematography.