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

Battle-hardened (25 points): Single player completed.
Elite Unit (25 points): Single player completed on Elite difficulty.
Exterminator (20 points): Killed 1000 aliens.
Frag-master (30 points): Killed 5 aliens with one Frag Grenade.
Hidden Treasure (10 points): Found all secret collectibles.
Immobilised (20 points): Stunned 5 aliens with one Stun Grenade.
Meat Grinder (10 points): Killed 250 aliens during multiplayer Survivor mode.
More Speed, Less Haste (10 points): 'Vengeance' completed in 17 minutes or less.
Seasoned Squaddie (20 points): Completed a level in multiplayer.
Survivor (10 points): Stayed alive for 8 minutes in Survivor mode.
Tank (10 points): Took 500 damage without dying.
The Informed (10 points): Picked up all the logs.