I agree with both the types of reviews, the horrible and the excellent, and here's why: I saw this movie as soon as it came out, because I am a Stephen King fan and loved the book. I didn't just hate the movie, I loathed it and was infuriated by it, since it bore no real similarity with the book, except for main characters, and even then, they were mainly just the names of the characters. I hated that Jack Nicholson played Jack Nicholson, when Jack Torrence was an essentially good man in the book, just weak. I hated that Wendy, a pretty strong woman in the book, who wanted to protect her son and if at all possible, keep her marriage, was portrayed by Shelley Duvall as a whimpering, weak woman. I watched several documentaries about the making of this movie and found that Kubrick felt no strong woman would have stayed with such a man as Torrence and so portrayed her as we see Duvall's performance. Further, Kubrick apparently didn't care much for Duvall so he basically tortured her to make her portrayal of the character even weaker than her part in the movie would have shown her. So, I hated the movie.
Then I started watching the documentaries in which the symbolism was pointed out. I decided to re-watch the movie with the mindset that it really isn't the Shining, it is simply a "jumping off point" for a movie Kubrick wanted to make. And I found that, when I stopped viewing it as a movie about a book and saw it as only a stand alone movie I actually liked it. Jack Nicholson portrayed Jack Torrence as crazy from the start; no subtlety was intended and no subtlety manifested...everyone was in danger from the beginning from an unbalanced man who was acted upon by either his own demons or demons in the hotel acting through him.
I urge those who hated the movie because of what it did to the book to try watching it as though it really isn't based on the book, because it really isn't. As a study of one man/family's unravelling, I feel it's a pretty good "horror" movie.