Mission 1: The UAC

The game immediately dives into action! Shoot 'The Possessed', as these zombie-like soldiers are called, then use the console and go through the door. Interact with the Praetor Suit to put it on. It's good to know that your (laser) pistol has infinite ammunition and that you can hold L2/LT for a more powerful (charged) blast. Use the pistol on weak enemies, like The Possessed and Imps.

In DOOM you have access to an automatically updating map in your Dossier, under Mission. Any important items you've found here are marked yellow, ones you haven't found are grey. Item locations can appear on the map when you walk close by, allowing you to pinpoint them.

Continue through the hall and kill the first Possessed with a Glory Kill by pressing the right stick. A Glory Kill (more like Gory Kill) is a melee attack that can be initiated when an enemy glows blue (after being weakened by your weapons). It turns orange when you're close enough for the Glory Kill. Performing this move grants a small health pickup. Kill the others, then collect the Combat Shotgun and go through the door.

Be on your way and defeat the Imps as you progress. These are agile and hurl fireballs at you, but can also claw you when they get close. Move sideways to avoid their fireballs. When you reach the large room, first kill all Imps, then look around for loot and armor pieces. When you've got a good idea of your surroundings, go to the middle and destroy the gore nest. A lot of Imps will appear, so take them all out. There's plenty of loot around so keep on the move. Exit via the elevator to reach Mars' outer surface.

Drop down and move over the road on the right to collect the Data Log. These provide background story. Up ahead, drop down and kill The Possessed, Imps and Possessed Soldiers. The latter will shoot back, so be careful and stay on the move. Once you've cleared out the area, climb the walkway and go through the door (which unlocks after killing all enemies).

Turn right and look up; you'll see a small blue doll. We'll get to it in a minute. Follow the trail to find a body with the blue keycard. Hop onto the crate and use it to jump to the nearby ledge; it is just barely possible. Here you'll find Blueguy, the first collectible.

Collectible Blueguy

Head through the door with the keycard and grab some Frag Grenades and Shotgun Shells if you need some. Hop down and kill the Possessed in this area. Before you go down the hill, check out the cave to the right. Inside are a few Possessed - waste them, then check out the AutoMap device in the corner. This unlocks the entire map of the mission, and as a bonus, this one also gives you a scanning technology so that you note items (on the map) that you walk closeby enough. Very useful for exploration.

Continue through the cave to find the corpse of an Elite Guard on a platform at the end. Inspect him to find a Praetor Suit Token. These can be used to, well, upgrade your suit with nice perks. A very useful one early on is the Item Awareness one under Area-Scanning Technology.

Elite Guard

Head outside again and go down the hill, killing Imps that bother you (meaning all of them). Continue to the right and jump over the gap, then turn right again to find a Field Drone. These drones offer weapon upgrades. Choose an upgrade for your shotgun and head back to where you came from.

Drop down to the lower ground and check out the large round-shaped machine with yellow bars around it; there's a doorway you can walk through, leading to a lever. Pull it to open a nearby door with... Yes! A small portion of an original DOOM (II) level! Kill the Possessed soldiers. You'll have unlocked the entire level, which can be played from the main menu, under 'Classic Maps'.

Head to the dock in this area to find another Data Log (check your map as well - it should be marked since you're fairly closeby).

Go back to the drone and continue. You'll face several Imps and Possessed in this area. Shoot explosive barrels whenever possible. With the crowd taken care of, continue down the trail into a narrow valley. At the end, move into an optional tunnel to the left to find Classicguy.

Collectible Classicguy

Simply continue in the next area and wipe the place clean. Climb up on the machines, collect some armore and health, then proceed inside and hit the console.