First of all, I really enjoyed watching this drama, particularly because the plot was amazing and really easy to follow even though it was surrounded by a lot (and I mean A LOT!!!) of mystery which makes it really easy for the viewers to get hooked on the story, especially if you're a thriller kinda person (If thrillers aren't your thing, this might not be for you).
When it comes to the casting, the cast was all of great quality but I do have to give special props to Min Nam-Goong who I've been a massive fan of for years now and I really did enjoy the way he was able to portray his character perfectly.
With this, I do have to point out that I wasn't expecting to get hooked on this drama at the beginning because the first few episodes were a little slow-paced for my taste and I was feeling it would be a boring show, but I kept watching it, and it got way more interesting and believe me, it's real easy to get hooked on it. Aside from this, I'd also like to tell you that this show is not like any other crime-related K-drama. Usually, you know who's the good guy and who's the bad guy. Here, everything is so mixed up that you don't really realize who's the good guy and who's not.