If you have played past Sonic titles, you know that Sonic Team doesn’t go easy on the achievements. You will probably be wasting tons of hours to get all the achievements/trophies in their titles. This one seems to be no different.
Xbox360Achievements has the list of achievements you will be able to unlock. WARNING: There are some spoilers in there. So if you want the game to be 100% fresh when you buy it, don’t click the link.