It's really good. It's baisically a Korean 24, or MI-5/Spooks. And there's also a spin-off, called Athena: Goddess of War, that takes place in the same world with some of the same supporting characters (the RoK President and his staff), and at the same time.
I'll warn anyone interested that the first 3 or 4 episodes are kind slow (they pretty much just focus on the relationship between the male and female lead) but once it gets going it gets really good.