Understand this: OLDBOY IS AWESOME!
That's pretty much all you need to know, it's an incredible film from Park Chan-wook, the follow up to Sympathy for Mr. Vengance and the middle film from his Vengeance Trilogy.
Basically after being imprisoned for 15 years Oh Dae-su is released. Shortly after he meets a man who tells him he has 5 days to find his captor and discover why he was imprisoned in the first place. What follows is an amazing, mind-numbing and disturbing mystery tale that left me both horrified and amazed.
Needless to say a re-watch of this doesn't have quite the same effect, but it's still an amazing piece of art, yet again demonstrating Park's amazing skills and talent as a director.
I really don't want to explain too much of this away, not specifically giving spoilers but even hints at the different parts.
No-one can be told what Oldboy is, you have to see it for yourself. SO GO!! WATCH IT!!
Oldboy - 10/10