I started to watch it because of the tremendous cast that it has, I mean with Lee Jong Suk, YoonA, Kwak Dong Yeon, Yang Kyung Won, Oh Eui Shik, and more actors that I have already seen and they never disappoint HOW NOT TO WATCH IT, and God seriously this It's great, so far there are only a few episodes and I can already say that it's one of the best this year I swear, it's impressive, this is so well done, the acting is so amazing I get the chills, if Lee Jong Suk is in the drama, it is guaranteed that it's great.
UPDATE
Well, this drama is over and I love it, it's my favorite this year, the emotion and excitement I had when another ep was up, the anxiety generated by having to wait for another ep, wow it was quite a spectacular journey, the The first episodes were so exciting and so well written, the last episodes were mostly sad, because there were many unfair deaths. Miho, my girl, the only thing she did since ep 1 was love and take care of her husband and above all support him and be by his side and then they kill her, I can't believe they did that to Ko Miho, a spectacular woman, then we have the fake pyschopath who died so unfairly, without the world knowing the truth and suffering like this while the real culprit is in the United States living happily, his death was so unfair, and Dr. Seo and No Park too, and Hyejin who could never live happy without that husband of hers chasing her and spying on her UGHH Hyejin and Dr. Seo would have been together, how sad. Changho, we really felt that something went off, something died inside him, after Miho's death, I feel like he never was the same after that, now, Choi Doha, his death was more like emotional, dying just like thousands of other people have died because of you and you die like that... but well, I think that we are open to a 2nd season because we still want to know things and we want to continue watching, and really after ep 12 the drama took a big turn and very strong, after Changho left jail, things changed a lot and I really like it, I enjoy every single ep, from the beginning to the end and I'm so in love of LJK and Kwak Dong Yeon that Duo I mean, really, WHAT A POWERFUL DUO, well, watch this amazing Drama, everyone did so well, BIG MOUTH DRAMA OF THE YEAR.