Truly one of the best acted, written, scored, directed, and shot dramas I've ever watched. With that said I understand this drama isn't for everyone, especially if you're used to watching light and fluffy dramas. Even so, I recommend this show wholeheartedly, but keep in mind that the overall tone is heavy and mournful.

Story
What I enjoyed about the writing was that it felt real and raw. I could believe the dialogue between the characters as actual conversations versus lines on a page. What I usually hate about the writing in dramas is that the characters are too one-dimensional, inconsistent, or simply don't change. Not here as you will find complex and authentic characters, no doubt helped by the excellent cast. The only thing I disliked was how Jin Kang was perhaps a little too forgiving of the people around her for acts that were quite heinous, which felt unrealistic but perhaps that's just her character trait.

Acting
I say with confidence, every single actor here was amazing. I've watched Jung So Min before in "The Sound of Your Heart" where she was quite funny, but this role transformed how I see her from now on. She has a special mix of charm, strength, heart, and humour. This is the first time I've seen Seo In Guk in anything, and I was speechless. He completely transformed into an enigmatic, tender, and dangerous Moo Young. Overall extremely impressed by the entire cast.

Music
The orchestral and instrumental pieces really elevated the scenes they accompanied. Definitely far better than average background music. I actually want to buy the OST.

If you can't tell, I really loved this drama. It balances the mystery, drama, crime, and romance very well. Production value is high here, and you'll be able to tell as soon as you start to watch. Just a warning, don't watch if you can't handle serious and tragic themes which can affect rewatch value.