Director Robert Aldrich [The Dirty Dozen, Hush Hush Sweet Charlotte] delivers what I believe is a perfect film. It's his version of Alfred Hitchcock's Psycho. Everything, and I mean everything, about this film works. The acting is stunning, the script is clever, the tension is unbearable and the cinematography is spot on. There is nothing to dislike about this film. It's an amazing study in human nature with its themes of jealousy, abuse of the handicapped, and mental illness.
This film is definitely a high point in both of these great actresses careers. You simply can't take your eyes off of them. This is one tense story whose images will stay with you long after the film had ended. If you've been living under a rock and have never seen this movie before, put it at the top of your list.
As an added bonus, character actor Victor Buono [The Stangler, Beneath the Planet of the Apes] give a delightful performance as Jane's new accompanist who is supposed to help her restart her career. It's obvious it's just not going to happen and he play off of Davis' illusions of grandeur very well.
For more info check out the film's entry in IMDB.