My theory is that there is a lot more to the Boltons that appears at first. Initially, yes, they are just another northern house, like the Greatjons, Smalljons, Umbers, Karstarks.. then there are the rumours of flaying, the monstrosity that is Ramsay Snow/Bolton, and then the more and more prominent role played by Roose Bolton himself. I got intrigued.
And then we start getting some clues, planted here and there by GRRM: Roose Bolton is always described as incredibly calm and cool, with eyes of grey ice. I think it's the eyes that got me intrigued. Why insisting on those eyes? They seemed like Others eyes to me. And then the leeches, like some sort of reverse vampire, trying to keep his blood cool, or thinned, or something. Then the ambivalent relationship with his bastard Ramsay. Then there is the episode of
What's in this book? Books aren't burned willy-nilly in those days. Must have been a pretty serious thing in there, some secret that he wants no one to find out?
So I read other threads and discovered other people are wondering about the Boltons as well. My theory is that there is a link to the Others. Left-field, yes sure, maybe. But the eyes man, the eyes!! And the smooth skin, the extremely soft voice (surely unusual for a man of his stature and position, for leading men surely you need a strong voice?). This leads me to believe that Roose Bolton is a much more threatening creature than appears at first, and that his conflict with the Starks goes back way before the Game of Thrones begins, and maybe dates back to the time when Brandon the Builder (a Stark) built the Wall to keep the Others at bay.
Maybe there has always been conflict between Boltons and Starks, and maybe this conflict dates back to when the Others were pushed back by the First Men (to which Starks say they are descended from). Maybe the Starks are skinchangers (wargs) and maybe the Boltons have been flaying Starks to wear their skins and get in the skinchanging game as well, or something.
I just can see Roose Bolton getting more and more power as the books progress until we can't avoid him anymore: he is gonna be a major force and even the Lannister and their allies will seem small beer compared to him.