Unlocked Cheats per Completion of Difficulty Level
Hard Difficulty - Finish all levels on NORMAL.
Infinite Ammo Cheat - Finish all levels on NORMAL with an A grade.
Infinite Shield Cheat - Finish all levels on HARD.
Infinite Health Cheat - Finish all levels on HARD with a C or above.
Infinite Grenades Cheat - Finish all levels on HARD with a B or above.
Choice of Left Hand Weapon - Finish all levels on HARD with an A.

Unlock Movies
The movies in the THEATER unlock after you have seen them, except for the first 2 movies which are unlocked after Deep Level. No movies are unlocked on EASY.

Unlock Extra Image
Each "A" grade in NORMAL and HARD unlocks an image in the image banks.

Secret Objectives List
Basic Training - Press every button in the end briefing room
The Drop - Kill the courier
The Push - Man the pintle gun and kill the 4 guards activated
Watch Towers - Kill all the snipers on the upper ring of the prison
The Cells - Free all the tau prisoners
Deep Level - Pick up the bread in the caves
Unwelcome Guests - Save the air caste in the kitchen from being killed
The Invaders - Save the air caste in the medical bay
System shutdown - Kill the 3 tech priests by the keys
Diversion - Find the 3 hiding air cast on the bridge deck
Clear the Decks - Shoot a barrel on a ledge on Deck B
Power House - Do not set off the sentry alarms
Distant Eyes - Kill the 4 snipers running on a ledge by the orange door
No Rest/Wicked - Shoot the barrels in the sewer
Silence the Guns - Kill the scared servitor in the engine room
Last Chance - Kill the 3 imperials you find as you jump down the stairs
City in Tatters - Kill both obliterators
Titanic - Shoot an enemy on the upper balcony from the middle balcony
Descent - Find the meltagun
Convergence - Find the 3 dead tau
Face of Chaos - Shoot the 4 chaos candelabra