Faster reload:
Immediately after pressing L to reload, press L3 to block. 
When L3 is released, your weapon will be instantly reloaded.

Extreme mode:
Complete the game under the normal or hard difficulty setting to unlock the 
extreme difficulty setting. 

Completion bonuses:
Complete the game to unlock the "Trailer" option and all entries in the "Gallery" 
and "Sound Test" screens.