Extra Game Modes
Complete the game once to unlock "New Game+" mode, which allows you to start the whole game again but keep your level and inventory from the game you just finished. Clear the game with an "A" rank on normal difficulty to unlock "Quest Mode."
Complete the game but don't skip the credits; if you watch them you are rewarded with the "Odd Job" mini-games.
Once you have completed the first four of the "Odd Job" mini-games you unlock the "Second Amendments" mini-games.
Secret Missions
Earn an "S" rank for the "Out of Control" mission to unlock the "Drunkard" bonus mission, providing you received an "A," "S" or "B" rating for all of the previous missions. Receive an "S" ranking for your performance on all the case files and you will unlock a secret mission in case 5. The mission involves killing the sniper family.
Weapons
Clear "The Woman Left Behind" mission, receiving an "S" rank for your performance, to unlock a 50-caliber machine gun.
There are two ways to unlock the mini-chainsaw: either get an "S" rating for the "Out of Control" mission or the same rating for "'The Shadow Of North Plaza" mission. Clear the game in less than ten hours with at least an "A" ranking to unlock the Chicago Typewriter. This gun appears in "Resident Evil 4." Earn an "S" rank on all of the "Odd Job" mini-games to unlock the laser sword.
Costumes
Complete the game twice on hard difficulty, receiving any rating. You can now wear the Kung Fu costume. There are two ways to unlock the Mall Employee costume: either receive an "S" rank in the "Out of Control" mission or simply complete the game. Play through the game killing at least 53,594 zombies to unlock the Apocalypse Frank costume. Clear the game without dying once and you can kill zombies wearing Arthur's boxers. Play through the whole game on normal difficulty and earn an "A" rating to play the game in a bikini.