It seems almost as if Stephen King wrote the novel this movie is based upon specifically for Jack Nicholson. He fits so well in the role of Jack Torrance - with his looks, his facial expression, his voice and his hair - you could think it was created only for him and noone else. Just trying to imagine someone else in place of Nicholson is pure insanity.
Of course, just like the character of Jack, the whole movie looks like the perfect horror movie. To me, there is hardly anything that even touches this film as to scariness and horror. All the stuff I used to be frightened of before this movie now seems like the boogeyman compared to it. It's just the combination of Stephen King's fine sense for the terrifying and Stanley Kubrick's incredible ability to get the maximum out of any story that make this movie what it is: A redifinition of the whole Horror genre.
This movie is THE milestone in 20th century horror history. It's still old-school horror, but on such a high level, you won't believe it, until you see it.