I think the main couple matched each other quite well because because the man is rather cold and the women is warm. In my opinion they match each other also quite well from their looks. From the first episode on I was so into the story that I didn't even want to stop it.
Up to now I've watched it over 4 times and I plan to watch it again soon because it was so nerve wrecking and I felt like this drama was real because the actors did such a great job with their acting. I also liked the mysterious part of the drama and also that you're able to think with them and also make your own thoughts about who the murderer is.