Firstly, I am a fan of Lee Dong-Wook and Wi Ha-Joon, that being said it was a little unrealistic, and though I like the show if I had to compare I like Stranger from Hell more than Bad and Crazy. (both have mental health as a prime factor in the main story)
I get the whole split personality story, and I like it. I believe in the whole take on why Su-Yeol developed a split personality and why it did not reoccur until the point in time when it did.
But, I am more than a little disappointed with the story of Shin Ju-Hyeok. The drugs and gaslighting plot line is plausible in the present time of the story, but my issue is with what he did years before when he killed his father. What he did in the past is the same as what he is doing now, which brings me to my question, isn't it too far-fetched to say that he was capable of gaslighting someone then? I get that he does it now, it can be deduced that it is a result of him studying psychology later in his life, or maybe it was through his experiences that he is able to gaslight someone and make them murder other people, but showing that he was always that smart seems like a stretch.
<Also, I was screaming at my screen since like the 8th episode that the psychiatrist is behind all of this, lol. I am also irritated to see how easy it is to manipulate facts. The whole force was corrupt right from the start of the show. >
Back to the story, it's entertaining, The scenes between Dong-Wook and Ha-Joon are comedic mostly which works. There are a few plot holes but if you aren't an investigator, you will get over them, the only downside is the ending. It all works out, but the way it does is rushed. I want to know how Ju-Hyeok always was a step ahead of everyone, he knew of every possible way someone could fk him over, and be prepared for everything until the last moment. And we did not get to see the proof that he was the one who gave his patients the drugs; if that actually happened.
It's not a bad drama, maybe it's just my opinion, but something was missing which could have made it the best. It's definitely worth watching, tho.