Vomitoreum with 90% discount on Steam

They are all pretty good, can recommend all of them.

FPS games like the original Doom or Quake. You run around, shoot everything and go to the exit. Little emphasis on characterization, or plot, few if any RPG elements.

Boomer is a person born during a baby boom - different time for different countries but these are pretty similar by years.
Shooter stands for FPS.

Boomer Shooter just means the game is similar to first Doom or Quake or Duke Nukem 3D or Wolfenstein as that was the games we played when we were very young and our first FPS games.