Complete the following achievements to unlock Xbox Live Gamerscore points:

Armory (10 points): Collect gout different weapon power-ups.
Bulletproof (25 points): Complete the game in Arcade mode using only 1 credit.
Full Assault (30 points): Complete the game in under twelve minutes.
Infiltration (15 points): Destroy the alien tower at the end of the water level.
Partnership (20 points): Complete the game in Xbox Live Co-op mode.
Proficient (20 points): Complete the second tunnel with a score of 100,000 or more in Arcade mode.
Team Work (10 points): Score 100,000 points in an Xbox Live Co-op game.
Tunnel runner 1 (10 points): Beat the first timed tunnel with 33 seconds or more left.
Tough Guy (20 points): Get to the second tunnel without obtaining a single weapon upgrade.
Tunnel runner 2 (15 points): Beat the second timed tunnel with 55 seconds or more left.
Untouchable (10 points): Get to the first tunnel without losing a life.
Well Equipped (15 points): Collect three different weapons in the second tunnel.