We have a couple of members who were based out of South Korea. I'm sure if they see this they'll chime in.
From what I saw the resorts were pretty basic. Not world class (cliffs, huge chutes, terrain parks etc) but serviceable. My hunch is that if you are willing to huff it a little, there is some pretty amazing terrain that can be had. Of course I know very little about the South Korean scene, so there could be same pretty bad ass resorts there.