I hopped on the hype train when I saw all those 10/10 reviews, but this certainly did not live up to the expectations for me. Here are my thoughts after watching the drama, as a dissenting opinion to all the 10s in the reviews. I would recommend watching Flower of Evil, but don't expect too much like I did.

The first few episodes set the stage for the story, leaving you wondering what each characters' motivations are. However, as the drama progressed, new characters were introduced and they start to become plot devices just to push the story forward. Without spoiling too much of the plot, I felt like the damsel in distress sister and the comatose guy had highly convenient relationships with the main cast that would just be ridiculous in reality. Also, the whole human trafficking side plot was unnecessary...

There is some suspense of belief required here, as this is absolutely NOT a realistic drama. Of the several crime/police dramas I have watched before, this does not rank high. If you're watching this merely for Lee Joon ki, Lawless Lawyer has a much better and believable drama structure. I understand the need in Dramaland for some coincidences, but this drama has one too many. After a few near-death experiences, trapping Lee Joon ki in a burning building doesn't make my heart race anymore because you know that he is effectively immortal in Dramaland anyway. Skip 20 seconds of burning building footage and his wife will magically appear and save him. Towards the end, I also found myself skipping the romantic scenes to get to the end of the story. I just wanted to know how the good guys and bad guys stories end, and everything else was filler to me. Blame the writer for writing it this way, but there has to be a better way to cause conflict.

Overall, I agree with the consensus that the cinematography and directing was superb. However, the writing was a bit questionable, as it got pretty repetitive later on. If you're new to police dramas, there are much better ones than this. If you're looking for a melo disguised as a thriller, there are also better ones out there. Once you've watched those, come back for this one - it's not bad, but definitely not worth a 10.

*SPOILER*
Throughout the entire drama, I felt like the idea that Do Hyun su is not a bad guy is forced down our throats. Everyone's actions are very one-dimensional - all the police were always against the homicidal monster, while Hyun su's side was continuously trying to drive the narrative that serial killing does not run in the family. While the premise was interesting pre-watch, I think it got tiring towards the end when it was the exact same Good vs. Evil trope.