Complete the game on the easy difficulty setting to unlock Art Gallery 1 and the Cabal guns.
Complete the game on the normal difficulty setting to unlock the .50 Desert Eagle and the hard difficulty setting.
Complete the game on the hard difficulty setting to unlock the Molotov cocktail and the expert difficulty setting.
Complete the game on the expert difficulty setting to unlock the rocket launcher and Cabal rifle.
Complete instant action mode on the easy difficulty setting to unlock the Cabal SMG and the Art Gallery 2.
Complete instant action mode on the normal difficulty setting to unlock Extra Adrenaline.
Complete instant action mode on the hard difficulty setting to unlock Extra Health and the expert difficulty setting.
Complete instant action mode on the expert difficulty setting to unlock Extra Ammo.