Confession: I have not seen "Oldboy." It is on my Netflix que right after "The Tudors Season One" and "Night of the Comet," really. After seeing "Thirst" I might have to move it up because I really like this guys style: which is bloody, sexy, more bloody, and visually arresting.
A young, idealistic Priest signs up for a medical experiment to find a treatment for a dreaded virus that has a 100% death rate. Part of the virus includes loosing copious amounts of blood (I hate that) and when the Priest starts spewing forth the red stuff he is given a blood transfusion. Well, this bastard donor happened to be a Vampire and although the Priest is cured of the vicious disease, he is now among the undead. Now, anyone would have a hard time adjusting to being a Vampire, but imagine how hard it would be for a man of God... pretty fucking hard. Now the Priest has to deal with bloodlust, sexual desire, people wanting him to make them Vampires. Of course, there is a girl, and this girl is CRAZY. Big time. And the poor Priest, a sucker is there ever was one (pun intended) falls for her hook, line, and sinker.
"Thirst," from the Priests point of view, deals with the philosophical and moral dilemma of being a bloodsucker. The filmmakers don't hit you over the head with this (the Priest isn't a brooding, Edward "I hate being a Vampire" sort) but it is the central theme of the film. What I really loved about this film, and I haven't seen much written about, is the fact that it is a Vampire Film Noir. Its "Double Indemnity" with fangs! There is a sucker (The Priest,) the Femme Fetale (Tae-ju, the woman who seduces him,) the plot (get rid of the husband,) and the payoff (comeuppance and redemption.) I could see this being made in the 40s with William Holden as the Priest and Joan Crawford as Barbara Stanwyck. It would be a lot less bloody but just as crazy.