Unlock Xbox Live Gamerscore points, by completing the following Achievements.

Achievement	How to unlock
Reunited ( 15 points )	Find each member of the Howling Commandos on Captain America (Single player only).
Stars and Stripes ( 30 points )	Defeat the Red Skull in the Final Clash mission series on Captain America (Single player only).
The Cosmic Cube ( 5 points )	Use the Cosmic Cube to your advantage on Captain America (Single player only).