Completely blown away at how fantastic this series truly is.

Production? Top-notch: The filming/directing is incredibly good, and the music is excellent as well.

Acting? Phenomenal: I'm almost at a loss for words to even describe this. The main male lead did an outstanding job with the role he was given, and both the chemistry and the tension between him and the actress who plays his wife were literally palpable.

Relationships? Refreshing: There is a little bit of romance, but aside from a minor kind-of-sort-of thing going on with a side couple, the main part you see is actually between characters who are already married and have a child (plus some flashbacks of theirs, which are serious and/or sweet, not cheesy at all), which is honestly a breath of fresh air.

Plot? Utterly gripping: It's a crime thriller at the top of its game. (And, as such, there are a few trigger warnings: Blood, wounds, drowning, psychological stuff, personality disorders, genuinely scary serial killer, etc.; however, none of it is gratuitous-- I don't really like violent media all that much, but I was able to watch this just fine.) Both of the main pillars of the story-- the crime thread as well as the character/interpersonal thread-- were so compelling that I was on the edge of my seat the entire time and marathoned the entire show as fast as I possibly could.

This is not only the best K-drama I've ever seen, it's one of the best shows I've seen of any kind. It's a masterpiece-- and if you haven't already seen it, you need to, right now.