Films influence films. Ideas build on ideas.
I created this as a series of lists on lbx. Those lists include notes on why each film was included and its significance:
https://letterboxd.com/chadman/list/horror-100-the-classics/
The point of this list isn't just to list movies that horror fans should watch. Its easy to find something like that. Its also not about the best films. Hopefully, this will provide an order for someone new to horror (or even an old hand) to experience these in a way that works best. To avoid watching Stereo and thinking that is a good example of David Cronenberg. Or watching Cabin in the Woods without seeing The Evil Dead first.
Part of the point is that chronological release order is not strictly the best way to watch films. Despite that, The Classics are still the place to start. Many of these introduce important film genres and some are even the best examples.