I mean, they're relaxing and all, but when I want something ambient and backgroundy, I personally prefer, say, Dreams of Dying Stars, or Blut Aus Nord, or some ...And Oceans, Borknagar, Ulver etc.
Some of those aren't actually a million miles away from Sigur Ros, they just have elements that make them more appealing to me. I could listen to Sigur Ros easily, it's just I choose not to.
Hell, can you imagine someone who couldn't stand listening to them? That would be one tense mofo.