There is an American series based on the same concept but I have not watched it. Why? Because I thought it would be boring..And I thought the same about the korean drama. I started it as an afterthought because I had nothing to watch. What started as a pure pasttime ended as one of my fav drama of all time. To tell the truth, since I am starting to miss it so I am thinking about watching the American one (though I forgot its name and now have to search the entire internet for it). If I have to speak about Kim Nam Gil performance, It was phenomenal. His character is an introvert person which he definitely portrayed well and if i may go overboard since I like him, it was fantastic. His character was the best at pissing people off and he did that well. Moreover, as the story goes on, as he deals with more these lunatics living in this world, u get to see the progressive deterioration of his mental balance. The exploding of the accumulated stress, anxiety and guilt brought with each cases was perfectly written and executed at the right time. Moreover, the other characters also did well in their role and the acting was also perfect each in their villain or heroic character. The serial killer actors were so good at their character portrayal that it had me wondered if it did not affect them mentally afterwards ( which i hope did not happen). In overall, this drama is a must-watch and cannot remain on ur plan to watch list.