Doom's violence is pretty vanilla by 2016's standards
But back in 1993? Doom scared the oaky, buttery chardonnay straight out of even the most progressive of parents.
Aside from occasional egghead games like Civilization, back then, video games still belonged to kids. They were designed for kids, and they were usually built by adults who still acted like kids. Bright colors, cartoony graphics, playful aesthetics, coins, turtles, etc. 1988's Super Mario Bros. 3-cartridge, for example, sold a jaw-dropping 17 million copies.
Then Doom showed up and crashed the in-progress kiddie party: it upended the punch bowl, ripped down the crepe paper, and delivered a Chuck Norris-style roundhouse to the clown's rainbow wig.
ID Software initially wondered (i.e., worried) if they could get away with what they were getting away with in Doom -- the blood, the gore, the shotguns, the pentagrams, the whole nine yards. Then Doom's sales went through the fucking roof. Then sales went through a dozen more fucking roofs. And everyone stripped naked, stuffed cigars in the corners of their mouths, and dove into their piles of money.