Gonna absolutely put everything behind
Sleepaway Camp.
One of the most imaginative and unique American horror films ever made, it plays with genre conventions (almost in a Lynchian way). It utilizes soap-opera drama to contrast with increasingly bizarre murder scenes, as well as dealing (tangentially?) with gender/sexuality issues. And the ending. My God. A master stroke that, in one jaw-dropping instant, recontextualizes everything that came before it, casting an instant haze of sickening confusion and creeping menace. Here's a little blurb I wrote for it quite some time ago if you're looking for additional backup on this movie:
http://enjoythemonologue.wordpress.c...rier-scariest/