I'm not sure at what point it dawned on me that the setting & vantage of Rear Window was going to be a fixture of the entire film, and not just a cute way to stage the first fifteen minutes — but that realization, and everything therein (the vignettes of every other "screen" having their own rising action and payoff, the incredible breaking-the-fourth-wall moment when Lars looks directly at Jeff, and by extension us) was so, so, so perfect. This was not just Hitchcock being really good: this was Hitchcock in conversation with what it means to watch something and to be watched in turn, and to have your viewership transform into protagonism. I half-expected a little twist that never came (and I think the movie is better for it; the points the movie is trying to make about Stewart's character are enhanced rather than diminished by the fact that he was right all along). Grace Kelly was great (let's set aside the twenty-one year age difference, and let's set aside the fact that I had to type "let's set aside the twenty-one year age difference").
I think genre films like this, if they want to be perfect, have to do three things: they have to utterly succeed at the basic level of telling an interesting story, they have to reveal something about the genre, and they have to reveal something about you. Rear Window did all three, and did so in a way that was utterly entrancing for every minute of its runtime.