I'm probably the wrong guy to post, because I lean towards old horror. I'm also not a gorehound.
BUT, if atmosphere and visuals are just as important to you, I have a few suggestions:
- Cabinet of Dr. Caligari: it's a silent film, and a little dry, but the visuals alone are stunning. The sets are pure German Expressionism and it's kind of a mind Fuck. Plus, Conrad Veidt's performance as the somnambulist is really disturbing.
- Dead of Night: a 40's British horror film that is an anthology with a connected centerpiece. More creepy than scary, but it works well.
- Island of Lost Souls: Still the best version of the Moreau story, and that's all because of Charles Laughton. If you let yourself get into it, it's really unsettling - a benefit of being a pre-code Horror film.
- Mystery of the Wax Museum: Not a great movie, but the two-strip Technicolor, the sharp dialogue and Lionel Atwill's performance make this really memorable. It's another pre-code, so they push the boundaries of the time.
- Freaks: You'll probably feel dirty after this one. Real life circus freaks on film, a famous chant, and one of the biggest reasons the Hayes Code was created. This disgusted a LOT of critics of the era.
- Nosferatu: I'm biased here, it's a personal favorite. Tone, atmosphere, pacing and visuals are excellent. Depending on the version you watch, as this is a silent film, the music score can make or break this. For everything good Universal did with Dracula later on, Murnau did it better a decade before.