Blu-ray is to DVD what vinyl is to CD — that is, it offers an incremental increase in quality that somehow takes the viewing or listening experience into a new realm. Vinyl sounds more like live music than a CD can, Blu-ray looks more like a projected 35mm print than a DVD can.
The Blu-ray quality is more important for some films than for others — beautifully lit films with shots composed in depth, like The Searchers, take your breath away on Blu-Ray.
It makes a great difference with a film like Rear Window, much of which takes place in a single room. Hitchcock works hard, through lighting and composition, to make that room seem like an interesting place to be confined. It feels bigger and more inviting when seen in a Blu-Ray presentation, offering the compensations Hitchcock counted on for limiting his male star’s presence to one relatively small space.