As one of the major films of the Bronze era of horror films (70's, 80's and early 90's), you'd expect it to be mediocre, but really it's a well made thriller. I wouldn't class it as horror, though. Like most Hitchcock films, it's better seen as a thriller or a look into someone's mind than a horror; it messes with your brain, not your heart rate. Either way, it's a good film whether you get your brain in a twist or you faint in shock.
Review of The Shining
