It kept me at the edge of my seat almost the entire time even though there weren't really "twisted surprises". It was exciting and interesting and I almost never felt bored (and that's kind of rare for me). Having romance on the sidelines was a nice change, I guess. I didn't really feel it that much, or maybe I just didn't care, but it was okay. It was there as some sort of relief from everything else, rather than a main part of the story. The music wasn't memorable, to me, anyway. There were some scenes where I felt they could've played better music.
Overall, it was a different drama in some ways, and it was good. Great, actually, although the ending was rushed. I thoroughly enjoyed this drama. The cases, clues, character relationships, and how almost everything was connected were great.

--- below is some personal rant, don't mind it---
I had hoped to see more scenes showing the relationship development (and interaction in general) between the two brothers, as well as more concrete closure for the brother in the last episode... That's the main issue I have with the ending. In my personal opinion, they showed a couple of useless scenes that could have been replaced with more info about the younger brother and what happened to him (and his hyung) after he made his choice.