So because the player moves so quickly in Doom, and because most enemy attacks are dodgeable, the player can avoid a significant amount of damage simply by moving. A skilled player can often deal with large numbers of enemies sustaining hardly a scratch. This creates a feeling that’s quite rare in modern FPS: that you are powerful because you are agile, not because you’re a tank. This frees up Doom’s encounters to feature huge numbers of enemies, to vary scenarios by mixing in different proportions of threats, and to have huge, sprawling, often non-linear spaces that the player can traverse easily. There’s nothing quite like it today.