Just hours ago I finished this amazing drama. I absolutely loved the narrative and style of Signal and have much to say in praise of the show. I'll break this review down into two categories: 'the good' and 'the bad'.

The Good:
Signal expertly weaves a story that spans decades. The writers use a circular narrative structure to pull the audience in while not revealing too much about the past while the audience and main characters are in the present. Had they not done this I don't think the time manipulation that is so central to what makes Signal work would have been effective. The plot in general is well structured and well crafted. Every episode left me waiting impatiently to start the next and the way the different cases were interwoven gave the audience much to figure out as more details were revealed. The cinematography too is excellent. The mood, tone, and ambiance of the drama is expertly achieved and adds to the storylines by alerting the audience to a scene's overall feel before any dialogue is spoken. The acting too is excellent on almost all fronts. The three main leads especially deserve praise for their emotionally impactful and gripping performances. Personally, I felt that Jo Jin Woong carried this drama. He was beyond amazing as Lee Jae Han and without his performance I don't think the drama would have been as successful and popular as it is.

The Bad:
My main gripe with this drama is with its villains. Early on there are hints of a bigger bad guy than just the perpetrators of the crimes being investigated in each episode. When he is finally revealed it was not shocking and that was okay with me as I felt that he has been built up and foreshadowed well by the writers and so the audience was already predisposed to dislike him. However, this character remains so one dimensional throughout the drama that I felt like I was watching a villain from an old James Bond film. I wanted to know more about his motivations, his character, and maybe see some growth or doubt. None of that came. The character remained stagnant with no deeper motivations or character traits beyond greed. The villain was also strikingly immoral in a way I feel that few actual human beings are. What made the villain stand out as being poorly written for me was how well the writers had done with portraying the inner worlds and motivations of the lesser villains. The perpetrators of the weekly crimes had more interesting backstories and story arcs than the antagonist. This was evidence to me that the writers could write bad guys well and simply failed to do so with our main antagonist. I also took issue with the way Park Hae Young's profiling technique was utilized. His prowess for catching the bad guy was almost otherworldly and to pin all this skill on his talent for profiling seemed highly unrealistic. He was just too good at his job for it to be realistic. I felt that Lee Jae Han's detective techniques and skills were much more realistic and better fit the realism of the story.

Overall Signal was great. It was well written and gripping. However, the antagonist was poorly written and plot devices to move the story along sometimes were too obvious. I would recommend this drama to anyone who likes both the crime and time travel genres. It is not a thriller but it is well paced and leaves you feeling satisfied with its conclusion.