The File of Young Kindaichi

The basic premise of this series is simple: a high school detective helps the police solving cases (usually murder), with a side-theme of young love. I think this is the best of the genre, for several reasons.

Firstly, all cases are well-developed (at least the original series, the reboot - Kindaichi R may be less so), usually having a 3-5 episodes arc and intricate methods.

Secondly, the characters are well-developed. There is no superhero rescuer (well, one of them is, but he usually took a supportive role), which makes the story ... more relatable, if not actually more plausible.

Thirdly, audiences are usually given full information as the detective, allowing themselves to work out a plausible theory.

Fourthly, and perhaps most admirably, each action serves a pragmatic function and is acknowledged as such. Many shows of this genre offer exhilarating plots just to serve a underlining theme and stimulate viewers' senses (e.g. murders happened in vampire castles involving people being drained of blood). The genius of Kindaichi is that these actions all serve a practical function which is explained at the end (i.e. blood had to be drained because it serves so and so purpose, while simultaneously playing into the underlining theme). This makes the whole series more realistic and looks extremely rounded. I'm sure true fans of detective fiction would appreciate the last two qualities very much.