was stephen king a "horror writer"?

no....

his best works are actually science fiction, clearly, and that's the best way to understand him. he also dabbled in various types of drama, which allowed him to write substantive social commentary into his works, and his books are deeply psychological in the sense of getting into the heads of everything from rabid dogs to people with paranormal psychic abilities, but he's a science fiction writer, first and foremost and that is how history should remember him, as one of the most important authors of the 20th century.

the horror side of things mostly comes out of unfaithful film adaptations, much of it just plain out silly. and, if you're trying to understand king via the shining, you're really missing out. a lot.

a common theme in his writing is the idea of self-control, and i think that's what i remember pulling from him, as a child, more than anything else: good dogs that don't want to be bad and scold themselves for it, kids that can't stop themselves from lighting things on fire, adults that can't stop themselves from altering the future, etc. there's good lessons for kids, there, whether it's intentional or not, about grappling with concepts of actus reus and mens rea. 

i was maybe on the young end of things, but these are actually good books to give young teens to read, despite the reputation otherwise.