Overall I actually really enjoyed watching this drama, but I know a lot of people that didn't. I get that many people thought the storyline was messy and too complicated but that's why I enjoyed it as most kdramas I can guess basically the whole storyline from the first episode.
The acting is on point as expected from Lee Min Ho, Kim Go Eun and Woo Do Hwan and their characters are enjoyable to watch, especially Jo Young and Jo Eun Sub (both played by Woo Do Hwan) meeting each other.
The music from the drama is actually one of the best I have ever heard, the songs used are so good I listen to them a lot more compared to other drama OSTs.
The only reason I didn't give it a 10 for rewatch value is that I feel the mystery is what makes it worth the watch, if you know the ending I don't think it's as interesting and I can image it would feel like it drags on.
Overall I wouldn't suggest watching it if you're looking for something you don't need to focus on. I would definitely recommend this drama to my friends though.