This is a great film that discusses the mystery of perception. James Stewart plays a photographer confined to a wheelchair, and, because he is bored, he voyeuristically examines the lives of his neighbors in the apartment building. We only see these neighbors through his eyes. Therefore, when he assumes that the man across the courtyard has murdered his invalid wife, at first no one wants to investigate his theory, especially his detective friend. But the clues seem to pile up, leading Stewart's girlfriend and nurse (a wonderfully witty role played by Thelma Ritter) to lure the man from his apartment to investigate further. The climax is powerful, true to Hitchcockian form.
Hitchcock's films are quite different from suspense films made today. The primary difference is the method in which Hitch crafts suspense. It's slow--on purpose. The climax is more powerful because the viewer builds up tension throughout the first 3/4 of the film. In this movie, Hitch's goal is not to shock or horrify viewers, but put them on the edge of their seats in anxious expectation of the climax. That, in my opinion, makes a great suspense thriller.