I am not saying that you should, in any way, shape or form, like the show, or that you should change your opinion of it at all but I think your base assumption here: a good man, an effective policeman, an admirable person in any way? is flawed.

Luther isn't any of those things and I never got the impression from the show that you're supposed to think that he's any of those things. He's a protagonist, but he's not a hero.