I have watched more than fifteen k-drama's till now. But this is the fastest I have finished watching any drama. Why? I don't even know. The story is so amazing that if you start watching it you just can't stop. The excitement & curiosity of knowing what happens in the next episode keeps you attached to this drama. Most of the the things about this drama was great. This drama is so fun to watch. All of the things more or less makes makes though this is an sci-fi, supernatural drama. The story is simple & fun to watch. What I meant by simple that the story is easy to understand.
If you are thinking about watching it then please do so. I can assure you that you won't regret it for sure. And rewatching this drama will be also very enjoyable!