Doom
Screen size: 320 × 200
Everything is rendered with a 1:1 pixel ratio, as a result it is made taller using an old monitor with non-square pixels. Wall textures are not the same as in floors, and the automap is distorted.
Some of the artwork was created with non-square pixels in mind (note the fat face of the player).
Duke Nukem 3D
Screen size: 320 × 200
The level structure (such as walls or "flat" sprites) was shortened to compensate for non-square pixels. However, game sprites or HUD sprites have a 1:1 ratio.
The artwork for enemies was created with non-square pixels in mind. This is also true for the loading screen (note the oval nuke symbol), but the title screen looks stretched compared to the box art.
Duke Nukem: Total Meltdown
Screen size: 320 × 214
The level structure has a 1:1 ratio and game sprites are narrowed, mimicking the DOS game with an old monitor. However, the HUD has a 1:1 ratio, so it looks shortened in relation to the level structure or game sprites.
Like the PC version, artwork for enemies was shortened. However, screens or videos ignore any possible distortion (note the circular nuke symbol in the loading screen)
Duke Nukem 64
Screen size: 276 × 208
Everything is rendered with a 1:1 pixel ratio, so game sprites are too wide and HUD sprites too short.
The new artwork ignore any possible distortion (note the circular nuke symbol in the main menu)
Duke Nukem 3D (Sega Saturn)
Screen size: 320 × 240, 320 × 256
Everything is rendered with a 1:1 pixel ratio, so game sprites are too wide and HUD sprites too short. Some backgrounds were made taller (such as the loading screen).