Accomplish the indicated achievement to get Gamerscore points:

Camper: Reach 120 seconds in Wave 1 without dying on the default settings.
Flawless: Successfully complete Wave 1 without dying on the default settings.
Co-Op: Successfully complete Wave 5 in Xbox Live with another player on the default settings.
Co-Op Master: Successfully complete Wave 20 in Xbox Live with another player on the default settings.
High score: Reach first place on the game score board on the default settings.
Pterodactyl: Defeat a Pterodactyl.
Triple Pterodactyl: Defeat three Pterodactyls in a game on the default settings.
Versus: Reach rank 5 in Xbox Live Ranked Versus mode.
Wave 5: Reach Wave 5 on the default settings.
Wave 10: Reach Wave 10 on the default settings.
Wave 30: Reach Wave 30 on the default settings.
Wave 100: Reach Wave 100 on the default settings.