THIS IS NOT A ROMANTIC COMEDY! The photo, the descriptions, the trailers, all lead you to believe this is a romance. It is not. What it IS is a brilliantly crafted police/crime/psychological thriller. This is a show that will draw you in at the outset and not let you go until the very last notes of music have died down. I'll warn you up front that you really have to pay attention, because there is a lot going on. A lot of the names were similar and there were a lot of flashbacks. This show really speaks to nature vs. nurture, how much our environment contributes to who we become, choices that we make in our lives, and different components that can make up a family - straying from the traditional thoughts of Mom, Dad and kids to a family of friends, a brotherhood, a dysfunctional coupling of wounded/broken people.

Let me get the female lead out of the way - Jang Nara. She was very good as a tiny but somewhat tough police officer. I did wonder why so many Korean dramas use the "stalker" storyline.

The male actors in this make the show. Seo In Guk is good in everything I've seen him in. In this show he's got that cool demeanor down to an art, but when he shows his vulnerability, it's so touching. Park Bo Gum - WOW! He was absolutely perfectly cast in his role. That beautiful smile and the ability he has to switch expressions on a dime. When his eyes turned cold, I got chills. His character was immature in a lot of ways and he played that very well, looking to others for help and validation. The scenes with Seo In Guk and Park Bo Gum together were enthralling and oh, so powerful.
I've seen Choi Won Young in quite a few shows, and he played a completely different type of character than I've ever seen him do. He was excellent and I found myself fascinated in a weird way.
Min Sung Wook was the comedic relief in a lot of the scenes and was really good.
D.O. as the young Lee Joon-Young was chilling.
This was a great Bromance-type show, between the men in the police squad, the trinity of the three male leads, Seo In Guk's character's friendship with the art dealer. There was a lot of good-natured joking around but there were many instances that showed the real bond between the characters.
The writing - oh my goodness, there were more twists and turns in this than driving on a winding mountain road. Just when you think you've gotten something figured out, the writers correct your assumption by throwing something else at you. A few of the characters kept referencing a "happy ending" and I didn't see how that would be possible with this show, but I thought the ending was just perfect. There was the typical "gone for a year" storyline (so, are the majority of people in Korea just alone, waiting for someone to come back from where they disappeared to? When someone leaves for a long period of time, don't they call? What's up with that?!?!)
Finally, the music - in the BRIEF time the main couple was together (remember I said this wasn't a romance), the music was light and airy. Then there was the suspenseful music woven throughout. But the best thing about the music was when they used that one-note discordant tone, it just spoke of the evil that was coming. Very effectively done.
I, of course, would have liked more romance (there was one very well-done kiss to appease me a little bit), but that would have taken away from the effectiveness of this show. Everything about this show was amazing and I was surprised to read that it didn't do well when it came out. This may be because they didn't do a good job of explaining what to expect. This was a smart show, and if you're not in the mood to have to think, you would find this disappointing. I was power-watching this ("just one more episode") because I was so invested in the characters and wanted to know what was going to happen next. After taking a huge sigh of relief that I was finally going to be able to relax, I was sorry that it was over.