Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Against the Odds (25 points): Complete single player levels 1-5 on Elite difficulty.
Ain't got time to bleed! (20 points): Complete 'Interface' single player mission without using a health pack.
Born to Kill (10 points): Kill a total of 25 aliens in single player.
Break Out the Arsenal (10 points): Fire every weapon and use every item in single player.
Campaign Veteran (25 points): Complete all single player levels 1-5.
Elite Force (10 points): Kill 50 aliens in a row without taking damage in single player.
Fighting Light (20 points): Complete any single player level without using any items.
Hard to Kill (20 points): Complete CO-OP Assault level 1, 2 or 3 without either player dying.
Killing Spree (10 points): Kill 20 aliens within 30 seconds in single player.
Knowledge is Power (20 points): Collect all the logs throughout the game.
No Stone Unturned (10 points): Find all secret collectibles.
Team Veteran (20 points): Complete "Hydroponics" in Co-op Assault.