I wonder if Stephen King will at some point get credit as an experimental novelist. In Desperation and The Regulators, King does something I've never seen before: he tells different but similar stories, in a different setting, but with the same characters (playing different roles with differing levels of significance) and a similar villain. Or perhaps he could be credited with bringing some literary innovations to popular fiction, as in the narrative form of From a Buick Eight, or the metafiction of the Dark Tower series.
King's prose has greatly improved throughout the course of his writing career, in my opinion, and more and more he's playing around with structure, narration, and style. King's writing may be more craft than art, but he is a master craftsman.