While some horror movies are clearly kietschy (and we love them because of that) quite a few have won critical acclaim for their fine directing, lights, editing, and sounds. The biggest Oscar winner is Silence of the Lambs, though others have brought home multiple nominations and a few minor awards. Exorcist got 10 nominations, while Aliens got 7, followed by Sixth Sense (6) and Psycho (4).
Still, sometimes you just want giant spiders and slime.