I think you'll find most people on here are huge fans of schlock, as you describe it, as well as the classics you mention (The Shining, Suspiria, etc).I, myself, don't watch horror movies to be scared, I watch them for pure entertainment.I can be entertained by schlock like Zombie Holocaust as well as a classic like The Omen.I don't think I've ever been really scared by a horror movie, but ones that affected me on very first viewing include: Salem's Lot (1979), The Changeling (1980), The Evil Dead (1981), Invasion of the Body Snatchers (1978), Friday the 13th (1980), Halloween (1978), Black Christmas (1974), Jaws (1975) and The Exorcist (1973).I really don't think they have the same impact now as they did back when I watched them for the first time.If you want quality horror (and you don't mention that you've seen it), I'd recommend John Carpenter's The Thing (1982).
