Didn't even watch the whole first episode of Luther. In particular sadistic cruelty or violence really bothers me. Things I've seen or read can come back to haunt me in the small hours - sometimes for years.
But some people must enjoy them, which I do find disturbing.
When I worked at the library there was a perfectly pleasant, 60-ish woman who was very keen on a particular crime author. She asked me whether I liked the books, and I had to say no (although I enjoy most crime novels) because they always seemed to feature sadistic violence.
She said she enjoyed those bits!
It still gives me a chill to remember that, and it was years ago.