Don't Look Now (1973) -- Great acting and some really novel edit techniques (esp for the time period). Also it's clear that a lot of the story and filming was thought out ahead of time, with recurring imagery (the color red, the theme of water, the purposeful lack of subtitles in spots, and so on). Unfortunately, I had no emotional response to this movie. I did not care about the protagonists, I was not shocked by anything that happened, and the ending while cathartic for one of the main characters had no impact for me. Worth watching if you're a film person to study film technique but otherwise... I'm not sure.
I largely love it for the editing, techniques and formalism like you say. I became fascinated with how it compacts time into a singular, compressed moment, where all the repeating motifs, imagery, and events, accumulate into the single, inevitable event of death that appears to dissolve time and echo past, present, and future. Using a linear time-based medium to depict the communication of something that cannot be portrayed in and breaksdown time. It's rare that films involving supernatural elements try to depict the connotations of an alien presence rupturing and communicating through the laws of normality in such a detailed way, and I think I admire it for that as a horror film.
Could go on longer but don't want to tl;dr