* The unnamed protagonist of Doom 3 is probably actually called "Marine Transfer", considering that is what appears on the passenger list at the start of the game (alongside Elliott Swann and John Campbell).
** Classic Doom, the Arachnotron and Spider Mastermind have, compared to other monsters of similar strength, a disproportionately high chance of flinching when they're hit and being interrupted from shooting back. [[spoiler:They're giant brains on mechanical legs. Of course they're going to be less resistant to pain.]]
*** Which has a bit of fridge logic in itself, since a brain is the ONLY part of a body that cannot feel pain at all (it processes pain but actual harm done to the brain itself can't be felt)
*** Possibly it's not actually pain, but unintended spasms caused by the punishment being rained upon them, then?
* Doom is the sequel to Wolfenstein: there are two hidden levels from the previous game. Okay, sounds reasonable enough; however the enemies are [[GodwinsLaw Nazis.]] In a Doom game. That focuses on demons and hell. Think about that for a moment. [[AcceptableTargets It all makes sense, why wouldn't there be Nazis in hell?]]
** Also related is the fact there aren't any dogs in the secret levels. One wouldn't expect animals to be subject to the same punishment as the people that trained them.
* The final boss of ''Doom II'' is [[spoiler:John Romero's head on a stick obscured by a giant image of a Satanic monster called the "Icon of Sin"]]. Appropriately, it is the source of all the monsters you've been fighting up to now, [[spoiler:which of course is John Romero's duty as a game designer.]]
* People complain about the huge, clunky [=PDAs=] used in ''Doom 3'' as an example of zeerust when they should be using something closer to a smartphone, but it makes all kinds of sense when you consider the setting and context: It's an interplanetary mining operation involving joint private and military efforts, so they ''would'' issue their employees a heavy-duty, hard-to-misplace device with a highly visible screen and long battery life at the lowest possible cost.
* The fight against the Cyberdemon at the end of Doom 3 is a call back to the final boss at the end of Doom 2. A small area filled with continuously spawning enemies and a boss that can only be hurt by one kind of attack.

* In Final Doom the forces of Hell invade via a spaceship. Looks like another race somewhere opened a hell portal too.
* {{Lampshaded}} in the ''Doom II'' ending: the Marine wonders where all the bad people go, now that he just trashed Hell.
* The presence of chainsaws on Mars is also lampshaded in ''Doom III'', where several [=PDAs=] complain about chainsaws ending up on a decidedly tree-less Mars. (They were a UAC shipping error.)