Luther.
We watched the 4 available seasons, typically short per many series from the UK (S4 was only two EPs), it's scheduled for a 5th season.
Outstanding, Idris Elba is fantastic, as well as all the cast, the stories are compelling, it's funny, a little darker than I originally thought - I've seen it described as a mix of Sherlock + Columbo, but I'd say there's a decent amount of Criminal Minds and Hannibal in it as well, the cases are _very_ horrific. It has some fun with some plot points too, that for some might strain the SOD, but I found myself immersed enough to go along with everything. Excellent choice of music throughout the series, in fact, I scored a few of the tunes (rediscovered some old favorites).
From IMDB:
Luther is a brilliant but emotionally impulsive detective who is tormented by the dark side of humanity while hunting down murderers. Once the self-destructive detective knows the killer's identity, it becomes a psychological duel between predator and prey.