Really the gore is when the sin eater is eating people's sins and we see the inside of his body. Although this only comes in flashes and is brief it is quite gory.
Besides that its very low R-rated gore.
However the violence is a bit disturbing.
A guy crashes through a windshield. We see a trickle of blood from his mouth. He then rots away a bit.
A guy gets nailed to the wall by thick nails.
Guys slip and fall to their death.
A guy falls into water but can't get out because there's grates above him. Another guy finally manages to get one open.
Two people are hung by a contraption; one of which is saved.
A guy chases after and kills a lady (we don't see it happen, we hear glass breaking, a shriek as we black out). Another guy finds her later bloodied.
A guy is killed off screen (we hear groaning/shouting and see a glow behind the door).
Another guy stabs a guy to death.
A guy shouts in agony and his chest crunches in.