I've watched many of the films that you've mentioned (all the uncut versions that were out in the 70's and 80's) and have to agree that with all the technology and intellect in the world, there's few modern films that come close.
I spit on your grave
House on the left (some of us thought this was so bad that it was a snuff movie)
Suspiria (the music alone is yet to be beaten in this movie, let alone the shocks)
The Witch (was another name before they re-released and cut it)
The Exorcist
The Sentinel (scary as hell)
Carrie ( that last scene had everyone jumping out of their seats)
Scum (the rape scene)
Zombies Dawn of the Dead (tense, but perhaps not as shocking)
They were all shocking in there own way because they set the path for later shockers like Misery, Malcolm X, Irreversible, Kill Bill, etc.
Some of the war movies are shocking as well, but don't want to go on and on. Perhaps other fms can name some.
That all said, I think that the 70's definitely had a shock factor of it's own that is difficult to capture on film these days. They set the precedent that modern film makers are trying to capture. And whilst I agree that the shock factors may be firmly in place, the atmosphere and the differentiation is just not there.
But then maybe I've just seen it all before.
