I'm pretty sure that Body Double is one of the most misunderstood movies of all time. Many people call it a tribute to Hitchcock, other people call it a rip-off of Hitchcock, some people think it's a parody.... I think it's more than any of those things, I think it's an analysis. A humorous, insightful essay on Hitchcock... Kind of like something Godard might do, which isn't surprising when you realize that Godard is also a big influence on De Palma.
The distancing techniques employed in the film, the way he hams it up, the scenes where the internal logic breaks down in obvious ways, like the kissing scene near the tunnel, where the movie suddenly reenacts the famous hotel kiss from the second half of vertigo, at a very unexpected time with almost no set up to make the scene believable... All these things are intentional, designed to let the audience in on the fact that this is not just a straight forward movie (although it can be enjoyed that way). De Palma wants the audience to have some separation from the story so that they can look at the movie in a more critical way, and think about Hitchcock's movies from a different perspective. These distancing techniques also allow de Palma to get away with some pretty harsh/sleazy scenes, and that was necessary because the analysis wouldn't have worked any other way.
This is basically De Palma saying, "what if Vertigo and Rear Window had a baby, but the baby was born in the 80's and raised by a prostitute and a murderous pimp." The result is a fascinating movie that stands up very well, as long as you understand the intentions. If you take it the right way, it's one of De Palma's very best movies.
As a big fan of vertigo and rear window (vertigo is my favorite movie of all time), it was fascinating to me, to see De Palma, rework those story's, twine them together, and put them in a different context. I really enjoyed it both times I've watched it, and I'm pretty sure it's one of those movies that will just keep getting better with repeated viewing.