I hate the textures, but the level's pretty fun with three players. Look for the Spanker!
Gives you marines to fight on your side (two kinds) and two new (nasty) weapons.
Just what it sounds like.
Adds a MS Windows logo on the breast of your bobs. Kind of hard to see, especially when you're trying to kill someone.
Never played it, but might be fun with 2 or 3 players.
Just what it says. That last corner is a doozy!
Kill that nasty dinosaur! Work out those agressions!
Dark.
Lets you edit (and create) physics models for Marathon.
Lets you convert Doom and Doom II WADs to a form Marathon can use.