Devil May Cry 4 is one of those old-school gamer games. After beating it one difficulty, you will want to beat it on the next, and then the next, and then the next. You can upload your score to Xbox Live at the end of each level you complete, so many will just want to up their friend's score. Playing through again allows you to use techniques you learn later in the game throughout the missions. You can also continue to upgrade your character.
You must check this game out. BC Magazine are not a big fan of this genre but they ended up loving this game. Once you start playing this game, you will not be able to put it down.