Monster closets galore.
“Monster closets” were a mistake. Doom 3 featured corridors studded with them, these chambers hermetically sealed until a player tripped the assigned trigger, unleashing a shambling monstrosity, or ten. It was the barest form of scripting, and Doom 3 was fond of assigning such surprises to power-ups or normal-seeming space base doors (don’t they all), meaning players hesitated over their spoils. As a result, the game could seem exceedingly cruel. This really was hell.
Part of the joy of Doom 1 and 2 was that their nonlinear levels unfolded like puzzle boxes, meaning MCs blended in remarkably well. Locations included outer space outposts, backwaters of hell, and dystopian urban slums (in 2), each a shifting mélange of keycard doors, MCs and elevator platforms. Think the Hellraiser cube writ large. Half-Life, of course, arrived in 1998 and completely buried Doom and its clones and set us on the linear, story-based course that the FPS genre has followed ever since. HL2 only made the mold harder, still looms overhead as maestro, etc.
And this was the environment in which Doom 3 faltered. Tellingly, id announced in the lead-up to Rage that it would not include MCs. And it didn’t. The developer had almost learned its lesson. Monster “holes,” barred areas from which poured a stream of enemies, faucet-like, replaced monster pantries that merely disgorged once. Was this an improvement? It was certainly better for immersion and world-crafting, but still a bit annoying. Used to be, id just threw all the enemies at you at once and let you sort through the mess. That was the game.

As monsters and the halls they stalked became more detailed in the late 1990s and early 2000s, players expected more sophisticated level architecture to match, and no more cheap tricks. The surprising thing is how fun and swish the cheap tricks of Doom remain. It has a quickness that I don’t think has ever been matched. In 1 and 2, a wall sliding down to reveal a dozen Pinky’s elicited a chuckle (and a mashing of 1 for melee) instead of a groan at how much ammo this will drain. Doom 2 iterated the form further and turned the puzzle boxes into meat grinders, but the engine had so streamlined the process of blasting and killing that it never got old. Doom 3 expired like a heaping big tub of sour cream – albeit a tasty one while it lasted.
MCs reached operational status in Wolfenstein 3D (1992) but weren’t perfected until Doom 1 kicked down the door to first person gaming in 1993. We can look to Super Meat Boy and other modern day ultra-hard games that polish game mechanics to a similar degree to find spiritual cousins. Ninety percent of modern FPSs, it doesn’t need to be said, are such a slogging chore that squad/military/tough dude NPCs have taken to completing most of the missions for you, no questions or tips necessary.
In my day, we used chainsaws.