Cheat Menu:
Enter ?TJL BDFW BFGV JVVB as a Password, then start a game, press pause and go to the 'Features' option. Check out the selections! God Mode; All Weapons & Ammo; 100% Health; and Full Maps. There's an additional option of Level Warp accessible through level 32: hit the 3 barricades in front of the Exit sign (look for it in between the Soulsphere and the Blue Combat Armor) and then press the switch.

Humor after death:
After you die, notice that you fall but the screen won't go "blood red" until you press a button. If you wait and don't press anything, the messages at the top will get quite interesting...

Password for Level 29 (Outpost Omega): RMMJ JCGF QQT6 RY2B
Password for Level 30 (The Lair): V85? D9T7 9F?B B8VB
Password for Level 31 (In the Void): LMVG HOWR 3CKN X79C

Level 32:
In the Staging area, explode all the barrels except the first one (9 in total). Then, go to the teleporter to come back to the beginning. Explode the first barrel and hurry to the door behind you. If you're enough fast, you will be teleported to stage 32! (This is one of the most difficult stages in the game)...

Thanks to Revolution readers Jesse (Guppy) Weisberg, Chant Jeranian, Patrice Lefebvre, Pat 99, and Danny Newlon!