I enjoyed this show a lot and for numerous reasons:
1) Lee Je Hoon. I really enjoy him as an actor. I liked him better in this than Taxi Driver, because I love when he's a little goofy.
2) The Team 1 detectives. Can we talk about the friendship chemistry they had going on? I really liked that we got to see what brought them into police work. There was no weak link in this group, each brought something special to the show and to the team.
3) Multiple cases. Though, more often than not, the cases were horrific and heartbreaking, I prefer that over one case throughout the whole show. The cases got darker as the episodes went along. I think at about episode 5 there was a warning at the beginning of each episode saying it was for mature audiences.
4) A good ending. This drama wasn't too long or too short. Personally, I like the 10-episode format, less filler. And this show could TOTALLY have multiple seasons!
5) Costuming. Really great job with all of the clothing.
6) Some of the episodes had further information at the end about what happened with the cases, or Korea at the time.
7) A female cop. Good addition.
8) Cute romance. Definitely not the focus, but I didn't feel like it was wasting my time.
9) The music. Very Austin Powers-ish.

Just a couple of shortcomings for me:
1) Team 2 detectives. Every one of them was corrupt, and it went all the way up the ladder. They were blatantly obvious that they were corrupt. To have that many corrupt cops seemed overkill.
2) At the end, when Je Hoon's character got promoted, everyone was celebrating, including Team 2. Why were they celebrating? That would be the end of the way that they do business.
For me, those were the only things that kind of diminished my enjoyment. This was a very well-done drama, with some comedy, lots of drama, a bit of romance, and a team of policemen always fighting for right.