Nope, it's not just an Alfred Hitchcock movie. Psycho, by Robert Block, was just as creepy and weird before Hitchcock got ahold of it. Actually, the movie follows the book very tightly. Block gives us more insight into Norman's head than the movie does (though some of the info in the novel appears in the movie sequels) and even goes so far as to diagnose his mental disorder.
The biggest difference in the story is the physical characterization of Norman Bates. In the movie, he is a slim, neat, and physically well put-together. Only his mind is a bit of a mess. In the novel, however, Bates is physically slightly off. He's overweight, and a little unkempt. There's more of a match between the outside appearance and the mental state.
I find it scarier when there's a mismatch between what you see and what you get.