"Bride of Frankenstein" is the class act of horror movies. Karloff's greatest performance, brilliant sets, great score, wonderful supporting performances--and a rich vein of dry humor throughout. Nothing else comes close.
Two others in the old Universal catalog are The Wolfman and The Werewolf of London...both real classics.
Nosferatu, the silent movie was indeed one of the greatest as was Dracula with Lugosi.
In a completely different vein, I think one of the most horriffic films pre 1970 was Rosemary's Baby.
"Io sono stanco, sono imbigliato, and I wan't everyone here to know, there ain't gonna be no trouble from me..Don Corleone..Cicc' a port!"
