What are must-have features in a TV detective series before you get hooked?

The main character needs to have some sort of character defect, and the cases need to involve things that do not happen every day.
House is a caustic misanthrope, Sherlock is arrogant and anti-social, Monk is obsessive compulsive, Conan Edogawa is a high school kid who got his body de-aged to primary school age via poison.
An over-the-top main antagonist helps, too.

It has to be called Broadchurch

Of Scandinavian origin helps (most of the time).

Ahhhh, Monk. I miss that show.
Along with good character balance, the casting was good.
No story can pull it’s weight if poorly cast.