I loved JSA. I think it was the first Korean film I saw that didn't have some sappiness in it. Don't get me wrong, it's not a criticism of Korean cinema, it's just that some films had a sappy underlying scene injected into it that didn't fit in the movie (like the movie Shiri, which I thought was great, but flawed).
I haven't seen the revenge trilogy, but I've heard it's really brilliant. I plan to rent them. In fact, I think you've just given me an idea of what my entertainment for tonight is going to be. Thanks!