I finished Gap Dong awhile ago, and I'm still in a confusing withdrawal. It says something when I'm still thinking heavily on a drama days later after I've had a chance to watch other things and go about my life. The drama struggle I had with Gap Dong was one of the biggest I've had in recent memory. The overall story was compelling, unique, and well developed. When I thought I knew what was going on, Gap Dong knocked me flat on my face. That unpredictability is what I crave in a show, thriller or otherwise, and Gap Dong delivered. Lee Joon was perfect as Ryu Tae Oh. He was sadistic, as any good serial killer should be, but he was more than that. There was a depth of character beyond your normal villain, and he continued to grow and develop throughout the show. I especially loved the moments when his face would take on a childlike quality. Not all that intimidating by itself, but when he adds a murderous gleam in his eyes and a big grin, it's SCARY. I'm still getting chills just thinking about it. On the other hand, though, I maintained a lack of sympathy for all the other characters. Maybe that's harsh, but it was an intense struggle. I love smart characters that make decisions heavily based in logic and fact, especially when it comes to thrillers and mysteries (like Ha Woo Jin in Liar Game or Sherlock in BBC's Sherlock). It seemed to me that everyone was operating on half a brain. Maybe that was intentional (how is he going to kill people if they are smart enough to catch him?). I don't know. Regardless of what the writer's intentions were, I had a very rough time. Bottom line - If you are looking for an excellent villain story with lots of twists and turns, watch Gap Dong. I will echo what many others have said: Lee Joon is outstanding. But if you despise characters who make stupid decisions and come to illogical conclusions because of their emotions or personal biases, you might struggle just like I did.