Doom/E1M4: Command Control

Before opening the door ahead of you, open the discoloured wall on the left; this will immediately locate you a secret area with a medikit, a Backpack and a box of shotgun shells. Open the door ahead and you'll be in a large open room. Kill the Imps and marines, then snipe a few off the balconies above by blowing up the barrels up there. You can use the middle doorway to go through to a room where there's a lift up there, but don't use it yet. Follow the tunnel opposite the door you came out of to a large room full of enemies. Clear them out, then go up the lift and kill the enemies that come out of the room that opens at the top. Grab all the goodies then head up the stairs to the large circular outside section with the circular room in the middle. Don't go in it yet, instead go to the opposite side of the room and down the stairs. Clear out the enemies, and you'll be next to a slime tunnel. Facing the ledge where the Imps were on, go left for a Soulsphere, a rocket launcher, and several other goodies.

Run off the ledge where the Soulsphere was to be back in the starting room. Choose any way up to the circular room you like (all three corridors lead up there eventually) and approach any of the four doors - they'll open automatically, revealing a massive amount of Imps inside. Finish them all off, then pick up the goodies, chaingun and blue keycard inside. You'll now want to head out the circular area to the grey room (leading to a new area of the map, if you use Tab to bring it up). Go left first of all and kill the shotgun marines. Then, head right and work your way through the rooms, killing off the Imps, marines and Demons. You'll be able to pick up some more rockets and shotgun ammo along the way. You'll reach a point where you can't go any further, so turn around and head back into the room with the blue keycard door. Open it, and you'll be inside a maze.

Whilst you make your way through it, keep watching your back - there are lots of ways the many Imps and Demons in here can sneak up behind you and inflict some serious damage as you try and run backwards into them. The way you want to go is to the straight corridor, and follow it all the way down, then take a right, then a few lefts and you'll see the room beyond the slime pit if you went right at the junction before entering the maze. Grab the yellow keycard, then go up the stairs, press the button by the yellow keycard door to raise the bridge to the exit, then go through and across. Hit the switch to end the level.