DOOM is the 1993 shooter that started it all, and this is The Ultimate DOOM with every one of its four episodes: Knee-Deep in the Dead on Phobos, The Shores of Hell on Deimos, Inferno, and the extra-hard Thy Flesh Consumed. You play a lone marine after a teleporter experiment opens a door to Hell, and the job is simple: find the exit of each level while zombie soldiers, imps, pinky demons and cacodemons try to stop you. Levels are packed with locked doors, colored keycards, switches and hidden walls that slide open to reveal armor or a new weapon early, so exploring pays off as much as aiming. Five difficulty settings go from gentle to Nightmare, where defeated monsters come back. For more pixel-style shooting, see Time Shooter 2 or Blockpost.
Use the arrow keys to move and turn, Ctrl to shoot and Space to open doors and press switches. Hold Shift to run and hold Alt with the arrows to strafe sideways, press 1 to 7 to pick a weapon, Tab for the map and Esc for the menu where you can save and load. There is no up or down aim, so just face an enemy and fire. Grab the shotgun as soon as you see it, keep dodging fireballs instead of standing still, and let monsters hit each other so they start fighting among themselves. When you cannot find the way forward, check the map for a door you have not opened and look for the keycard that matches its color.
