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

Go Forth and Multiplay (10 points) - Play an Xbox Live multiplayer match
Nice Beating You (10 points)       - Play single player campaign mode, reach level 10
One Meeellion Blocks (10 points)   - Destroy a total of 1,000,000 blocks. 
                                     All blocks you destroyed from all levels are counted
Been There, Shot That (15 points)  - Use all 20 power-ups in the game, including the red 
                                     power-downs. The tutorial level doesn't count
Two Thumb Master (20 points)       - Finish the single player campaign
On A Gamer's Diet (20 points)      - Shoot 50 zombies, 50 robots, 50 pirates and 50 soldiers
Natural Born Gamer (20 points)     - Shoot 5000 enemies in total
The Things I've Seen (20 points)   - Shoot every type of enemy at least once
You Can Handle the Riot (20 points)- Reach level 50 in endurance or co-op mode
One Shot, Thrice The Score (25 points) - Kill 3 enemies with one shot