First up I know a lot of people dropped this drama early on and at times I can see why but you're really missing out on the greater part of the drama by doing this. The actual plot line doesn't start up until around the end of episode 4. The first few episodes are building up to the actual plot line and while I do think it's needed I think they could've shortened this prologue of sorts to at least two episodes.
I know a lot of people also dropped this drama because there hasn't been any romance...yet I don't get why people came into this drama for romance when the tags clearly don't have that genre listed. Anyways on with my review.

Story/Plot:
Gets off to a slow start but it sets you up for this dark story of Dongbaek, a famous police officer who has the ability to see people's memories through touch. Cool right? Yes and No. There are people who love him and idolize him and then there are people who hate him and don't want him to touch them in fear they'll get arrested for something illegal they did years ago. Despite Dongbaek having the extraordinary ability to see people's memories he himself does not remember his childhood memories past a certain age. The only memory he can remember is someone murdering a woman he assumes is his mother. The plot moves forward to introduce to us our female lead Sunmi, she is the daughter of a man who was murdered by a serial killer who seems to have come back 20 years later.
However, not everything is as it seems. There is actually a serial killer out there dubbed as the Eraser, who like Dongbaek has a special ability in which they can erase/manipulate memories. Throughout the entire series you are left questioning who you can trust and you can't as you try and figure out who exactly the Eraser is. And like I mentioned in the headline just when you think you know, you really don't. (I had so many theories going the entire drama.)

Acting/Cast:
The acting is/was amazing. I am a huge Yoo Seungho fan and I'm really happy he took the role of Dongbaek. He plays him really well. I am also a fan of Lee Seyoung, I really liked her roles in The Best Hit and Vampire Detective. I personally really like her in badass female character roles. I also want to mention Jo Sungha is excellent as always.

Music:
Sometimes the music is not needed but honestly that's something that's typical in k-dramas. I did like the ending theme a lot though.

Rewatch Value:
I already sort of rewatched it. I watched up to episode 12 by myself and then later rewatched episodes 1 through 12 with my mom until she caught up with me. I recommend watching it twice you catch stuff you may have missed the first time through it.

Overall:
I personally think if the prologue part had been shortened 2 episodes it would've kept people more interested. I also think that episode's 13, 14, and 15 could've somehow been consolidated into 2 episodes at the most, it felt drug out. It almost seems to me that they were originally going to go a different route with the plot but changed it last minute, as there is a scene in one of the episodes previews that does not make an actually appearance in an episode. I think this drama could've easily been better off as a 12-14 episode drama. The drama is wrapped up nicely though, definitely worth a watch!

Don't let this get you down though, the drama plot is really fun to follow if you are an avid crime/fantasy watcher.