I have to admit that I'm being an "Achievement Whore" on this game right now.
On the 360, there is the whole "Achievement" high score set-up thing. It's a system of extra points based on completing extra or specific game tasks.
Usually the points are weighted on Multiplayer, and since I don't have nor want XBox Live, I mostly don't worry about earning them...but since this game does have MP, the points are all based on singleplayer, and I'm trying to get them all.
http://www.xbox360achievements.org/guide.php?gameID=67