Unlock Extra Zone: When you have collected ALL 7 Chaos Emeralds and completed Sonic and Blaze's story the Extra Zone becomes available at the 'Character Selection' screen. In Extra Zone you play as Super Sonic and Super Blaze.
Unlock Sound and Time Attack Mode: Both of these modes will become available when you have completed the game.
Unlock Zone X in Time Attack Mode: When the game has been completed this extra level which is not available in Normal mode will become unlocked. It has 4 acts which are similar to Sonic 2's 2-Player stages.
Unlock Blaze as a Playable Character: Blaze will become available when you have defeated the first boss.