The horror/survival concept took some time to establish itself as a distinct gaming genre, but Silent Hill played a pretty significant part in defining that style. And that's really what Silent Hill games are all about - style. In many ways, this makes them both ideal and problematic for conversion to the mobile platform.
Ideal because fancy graphics and lightning fast playing speeds aren't a part of this series' requirements. The difficulty comes from imbuing the mobile versions with the same nightmarish vision that made Silent Hill so iconic in the first place.