Doom was what you could call The First Person Shooter. Not A First Person Shooter, but The First Person Shooter. And yet, many of its peers in later years have missed out on a core element that made Doom shine back then and still does now.

https://www.youtube.com/watch?v=BdeZT6d9fas

In-fighting?
Armies of enemies?
I sure miss than in most other FPS games.