Themed music/sound effects and stages to begin with, the best example for a 2D game is Splatterhouse besides the Ghosts'n Goblins/Ghouls'n Ghosts (the first 3 games), the best example related to CV is Super Castlevania IV good music and stages bad sfxs, another example for a 3d game is Nosferatu WoM for PC, that game has everything horror themed music/sfxs, stages.
I think Super Castlevania IV was to be released by 95' or 96', then maybe we had have a clone Resident Evil in the universe of Castlevania maybe, it is interesting to see the influence of Rondo of Blood changed everything forever.