Just watched Gwanghae (Masquerade) and it was excellent. It's a costume drama about a conflicted king who hires a double out of fear of assassination but is poisoned soon after, leading the double, a lowly jester, to take his place entirely.
While it starts off kind of serious it's actually a humorous movie, with the typical juxtaposition of a commoner against the royal lifestyle, who shocks everyone with his sudden change in demeanor. It's all very cliché but the movie works because it's extremely well-written but more importantly, features top-notch acting by the entire cast, especially Byung-Hun Lee (of I Saw The Devil and A Bittersweet Life fame) as the king and his double.
It's a lot different from all the gritty revenge stuff that Korean cinema brings us nowadays but if you keep an open mind, you can't go wrong with this one.