A stunning film, although would've been better without...
I just watched this movie for the first time, and was surprised by how well it lived up to the acclaim. It really is quite a haunting and profound exploration of psychosis, especially for its time. The performances and visual style is mesmerizing.
However, the more I think about it, the more I feel like the whole movie was undercut by that Agatha Christie-esque reveal about 3/4 through. I.e. that John's friend had hired an actress in order to frame his wife for suicide, etc. If they had taken that letter scene out, then all of that surreal, supernatural possession stuff would still be there, which I found to be some of the most intense stuff of the movie. In fact it wouldn't even need to be supernatural - it could have just been a person reading about her great grandmother's trauma and being viscerally effected by it the point of nightmares, kind of like a dark mirror to whatever repressed memories were causing John's vertigo. But instead it was just the product of a B-movie murder plot.
Don't get me wrong, it's still a brilliant movie, and there's nothing wrong with Hitchcock murder films, but it felt so much more ethereal and surreal up until that point. I wish they'd kept it that way. You wouldn't even need to change the rest of the movie - but rather than an actor being found out, it would be an innocent woman being tormented and eventually killed by the traumatized hero of the movie.