Successfully complete the game on the easy or higher difficulty setting to unlock Gallery 1 and the Cabal guns.
Successfully complete the game on the normal difficulty setting to unlock the .50 Desert Eagle and the hard difficulty setting.
Successfully complete the game on the hard difficulty setting to unlock the Molotov cocktail and the expert difficulty setting.
Successfully complete the game on the expert difficulty setting to unlock the rocket launcher.
Successfully complete instant action mode on the normal difficulty setting to unlock extra adrenaline.