The original Nightmare on Elm Street and Hereditary are the only movies I can think of that make me feel like a kid again when I watch them in the dark alone. Saw Nightmare when I was way too young and while I don't lose sleep over it like I did then, Freddy still gets to me. Can't believe how much Hereditary ***** with my head and makes me feel like a little *****. I know a lot of people think it's kind of goofy or silly and I can see where they're coming from but it still manages to get under my skin.
The first Halloween is probably the closest thing to a perfect horror/slasher you'll find. Stands the test of time and proves good horror is simple and doesn't need a bunch of CGI and other bells and whistles. All you need is a terrifying monster, straightforward simple plot and building tension. The episode on Movies That Made Us on Netflix is definitely worth a watch. Crazy how a group of young filmmakers with minimal experience made such an iconic movie with hardly any money or resources.
Don't want to do a whole write up on each movie but The Witch, the original Wicker Man, and It Follows are ones I've watched somewhat recently and really enjoyed.
Along with simplicity the often bad special effects in older movies imo stands up over time better than the recent ones. Like it was comically fake in many but it still does.
Seems like with CGI as it may look 'better' at the time tends to look worse later.