For me, it's about her sound, period. Just her sound and how it occupies its space, what it lets in and what it keeps out. It's very pleasing to me how it does those that.
Don't know that I could be more specific than that, or that I'd want to.
Having said that, some of her things are just too morose for my taste. Haven't dwelt on those long enough to decide whether that's on her, her backing, or the recording, or all of the above.
As ((rightfully) well-regarded as Dream Of You is, though, I prefer this one:
http://www.youtube.com/watch?v=rv3qIZ03mBI Ok, I can get more specific. I like how she handles her vowels. But then again, that's what I like about any singer of this ilk that I like.