Oldboy is good. I remember stumbling on the manga, binged it as fast as my modem-internet would allow me to, and was thrown for a loop at the end.
Fast forward a few years, the movie came out. I forgot all about the ending by that point, but remembered the emotional ride I was out through from the manga, so I watched it. It was another "f---" moment. It was good.
I think there was an anime on it too. Might've watched that.
Then the English one came out. The chick was pretty, but the impact wasn't the same. Different delivery. But I'd definitely rewatch for the chick.
I need to watch the other two series of the Vengeance Trilogy: Lady Vengeance and Sympathy for Mr. Vengeance.