Complete the following tasks to unlock the corresponding achievements and their alloted GamerScore.

Annihilator - 10 GamerScore:
Kill more than 85% of the total enemies in a zone.

Assault Hero - 30 GamerScore:
Complete the game.

Exterminator - 10 GamerScore:
Defeat the giant spider.

Lair Slayer - 10 GamerScore:
Complete ALL underground zones.

Sharp Shooter - 10 GamerScore:
Don't waste more than 30% of your bullets.

Unstoppable - 10:
Complete a zone without losing a life.

Small Arms Expert - 20 GamerScore:
Complete a zone without using grenades or nukes.

Peace Maker - 20 GamerScore:
Complete a zone killing less than 50% of the enemies.

Speed Freak - 20 GamerScore:
Complete a zone in less than 15 minutes.

Survivor - 20 GamerScore:
Complete a zone killing 60% of the units on foot.

Tricked Out - 20 GamerScore:
Max out ALL of the vehicle Power-Ups.

Twin Medal - 20:
Complete a zone in Co-Op mode.