When I watched it I was with a friend and both of us do not get scared from movies. When the first killing took place, we applauded cause we were bored only watching the girl driving her car for around half an hour. Watching one of the most rated 'horor' movies of all time, we were expecting some horror.
It is a good movie , no doubt about it but I agree that it isn't that much horror. Probably it has only that scene in the end of the movie when it can scare you a bit, but that's it. And always found it strange in Hitchkock movies, the conclusion, when someone explains what happened, just in case there are some idiots watching it who couldn't understand what's going on.