Easy way to Unlock ALL CharactersAdded 1 Apr 2010, ID #3611
Complete the game on the Easy difficulty setting but do not overwrite your save. Doing this will have unlocked two of the characters. Then go to the 'Game settings option and switch the game difficulty to Hard. Now go to Story mode and select 'Continue' instead of 'New Game'. This will play the ending and when the ending credits have finished the last two characters will become unlocked without you having to replay the entire Story Mode on the hard difficulty setting.