I'd think if they'd just keep up on the graphics, the corpses and monsters would do all that is necessary.
Well you would think, but Oblivion to me was kind of a case-in-point for why world-art doesn't directly correlate to fear, scares, or tension.
I mean, look at the world art in the Deadlands, or in necromancers lairs. In the deadlands, you had containers that were literally made out of (sometimes-still-pulsating) flesh, heads on spikes, charred-black bodies whose eyes and mouth were eerily fire-red from the internal magma-heat, wall textures that had blood and grime everywhere, sinister things like the corpse-masher, etc. And in necromancer lairs, you had plies of bodies everywhere, bits and parts all over, all of which had quite a bit of decomposition detail. And yet while that disturbing world-art worked its magic for a while, the player eventually got desensitized to it, until they forgot that shock effect was even there.
That's why the emphasis shouldn't go on how horrific the things look like, but on how you use those horrific things without overtaxing and overdoing, while using placement, lighting, and other ambiance, etc, to affect the overall mood.