I dunno when you seen the movie but there was no "build up" for me. I seen it around the time it came out in the U.S., fairly close to it's original release around '03. So there was very little hype surrounding it unless you were hardcore into info on foreign movies.
It wasn't like I went into it expecting a twist. I heard it was great, and was impressed by the direction, cinematography and acting. The twist was just some extra shyt. Take out the twist and you still have classic cinema like the hammer scene, the hallway fight, the editing when he's locked up, the octopus scene, etc. With the twist it's on another level.
"Sympathy for Mr. Vengeance" was aight. "Oldboy" and "Lady Vengeance" are his best movies. "Thirst" was aight too. That cyborg movie was trash.
If you like these kinds of movies "I Saw The Devil" is another classic.
Fred.