Good script, Good acting, Poor directing
Ya need all three to be a classic, but instead it is just another good movie.
The flow was just off in this movie. It seems that the director did not have any regard for audience reaction, or any sense of buildup. This movie is supposed to be suspense but the director has problems coming through. A prime example is the attempted murder of Alan Ralmy at his home. It was a downright horrible scene, no suspense at all, pretty sloppy. I think that the director was going for a 'chaos thing' but it just ended up looking lazy. She wakes up, Alan quiets her and says someone is in the house, a closet opens and he is attacked.
There was other examples, but generally I think that movie just did not build up enough tension/relase for the viewer. I wonder how different this movie would be if Hitchcock in his prime would have directed it.