I have yet to see this one, but I have seen the 1996 remake with Chaz Palmetri, Sharon Stone and Isabelle Adijani... I realoy liked it and want to see the original

Finally got around to seeing this classic. Blown away! Supposedly this film taught Hitchcock a thing or two (he was a big fan and was heavily influenced by Diabolique when he took on Vertigo).

Things I loved about this flick:

1. Nearly zero action on camera. No shootouts, car chases, and even the murder is mostly off screen with the camera capturing what's going on the other rooms instead. Brilliant, suspenseful storytelling that gets into your head, not your gut.
2. No music! Like the Fritz Lang classic "M" there's nothing to remind you you're watching a movie other than the camera & edits. Very effective strategy at psychological realism.
3. The surprise twist actually had a lot of visual hints throughout the film. So it wasn't just a sudden Kaiser Soze moment like modern plot twists go. When you watch it a 2nd time you see it clearly. Perfectly written, believable story.
4. Great use of visual depth. Characters don't just enter/exit frame from the left or right. They appear at the end of corridors and move around in the plane of depth. Very subtle but again very effective at immersing you in the setting.
5. Great characters. Every character from the leading star down to the 1-liner kids was really memorable
6. tons more but you get the point...

I'm over at letterboxd today and some are adding the film to their Hooptober watch lists. I wouldn't classify it as horror but it is pretty intense at times.