It will have spoilers (maybe a lot)!
First of all, I've had watched two episodes that I couldn't sleep after, that's the way the drama made me feel, anxious for a conclusion, anxious to discover more and more everytime I finished the episode, and this two episodes were when Park Gun Ho and Lee Dae Chaeol died. I think the first half of the drama is incredible, you are always afraid of what will happen and at some point we really wish the truth will be revelead, we have that human faith that everything will be fine, but just as life is, it will not. But I have to say that after episode 12 things it gets a little messy and when we discover the real culprit of the university student murder, it just gets tiring. From a personal perspective, a lot of things stayed without a proper answer to me, the story behind the family and the murder of detective Oh's dad, how it were the relationship between him and his cousin's family, also in the ending I thought it was unclear if detective Oh had killed detective Nam or just hurted him badly. Plus the wife of the detective that were killed in the church incident, she maybe ended knowing nothing about what really happened to her late husband, and how detective Nam was the culprit of killing his own coworker. I also think she should have knew about how her actions helped kill Lee Dae Chael that were innocent in the end and left his daughter alone...
The chief of Jeonghan's journal death still bothers me a bit because it seemed that he suddently, really suddently felt the guilty for the dead of a man he was responsible to help kill. Even 5 years after Lee Dae Cheol's prision sentence and with a second judgement going on he did nothing and hided proves that could have saved him, he just choosed to uncover it all. I still think about how he (knowing everything from an investigator and reporter view) thought that he killed the detective as he also knew that the result of the autopsy was a knife injury, if not would be certainly asfixia. Also I ask myself why the knife of the student incident dissapeared and appeared in the hands of the chief investigator and they knew nothing about the real culprit?
Despite it all that I have said... I loved the drama and I think the jewel of it is Kang Do Chang , he is a magnificent person, friend, also a leader to all those who work with him and he make even his superiors respect him, he is a human who cares about others and bring problems to his personal life in order to make things better, he is always doing his best.
Oh Ji Hyeok is also amazing, I think (as I said before) it lacked information about him because we can see him suffering mental health problems all the drama but this is not fully explained, like, why his dad died?...
Oh Jong Tae is a degenerated person until the end and I think things were solved for him really fast with a full life sentence but I still thought that, for someone who manipulated so much important people for all those years it lacked something, it all happened really fast in the end...
It is getting really long so I'll just say you have to watch this, it is a really awesome drama and I highly recommend it, I watched really fast and I could sure watch it again to spread the word of korean dramas to my friends!
For all the work team that made this drama happen, thank you!!!