Complaints I hear about modern horror films often are centered on the lack of practical effects and their replacement by CGI. The argument goes that so much of the blood and guts in these films are created on a computer, as opposed to using red corn syrup and sheep brains, and that it doesn't have the same effect as the old effects did because it lacks the presence and weight that you can see onscreen. Even if the red corn syrup looks super fake, it's clearly a fake something, captured on film, as opposed to pixels created after the fact. The actors can then really react to it and make it feel more integral to the scene.
I agree with this, to a point (clever animators can make CGI gore just as fun as practical gore if they use their tools right) but I think an even bigger thing missing from modern horror are the sounds. The squishes as somebody's intestines get ripped out, or the cartoony "SPLATS" of blood hitting a wall. If you watch Berberian Sound Studio you can see how integral these pieces of sound design are to the creation of a movie. Because it's not visual, however, these contributions often get overlooked by moviegoers still reeling from what they've seen onscreen.
Re-Animator, based on a story by H.P. Lovecraft, is a very gory movie. It has blood and guts all over the place, spraying out of a decapitated head or gushing from a zombies mouth. But more important then that, it sounds gory. Ever drip and drill, every squirt and screech, all are used to enhance the action onscreen in a way that turns the squick factor up to 11. A bloody head I can stand, but hearing the squish of the needle sinking into the neck as the plunger pushes it's serum into the body is a whole other world of disgusting, and Re-Animator knows how to uses these methods to their greatest effect. It's gross, and all the better because of it.