Well, I don't know about people in general, I can only speak to what I like about them. I like some oddball dissonant black metal, I like complicated melodic black metal, I like creepy industrial atmospheric stuff... Blut Aus Nord does all of it. I like their intuitive songwriting and the way they develop parts. I feel as though I'm being led through a maze sometimes. They're never boring to me; they never beat anything into the ground. I think their melodies are great; they have a particular melodic sensibility that goes through everything they do, which feels familiar to me now because I've been listening to them for a long time. I wake up or go through the day with some parts of their songs stuck in my head. Also, there's a meditative quality to their albums that always leaves me room to think, so I can enjoy their stuff and pay as much attention to it as I want, but frequently find myself using it as a soundtrack when I'm working, walking, doing dishes, etc etc. I can't think of another band that plays stuff this engrossing that also leaves me space for thought.
But, they didn't click immediately for me; it took me a few years. They play stuff you don't usually care for, and they're a bit dense and hard to appreciate right off the bat anyway, so it's no surprise that they wouldn't appeal to you with a few casual listens on the forum. I would not expect them to be your cup of tea.