I haven't watched Luther. In The Wire he's very reserved but calculated, the strong silent type. It takes a good actor to pull that off. Like Brando.If I remember correctly the series does get a little hinky somewhere around the 4th season, but it still keeps you wondering what happens next.
I'm nearly done with Luther, then I'm moving on to The Wire. Elba is so quirky and strong as an actor. I really like that. He moves like no other actor. That sounds odd but I wonder if you noticed that about him.