Here is the full list of all 21 Galaxy Bricks achievements.
Break 10 bricks
Broke a brick
Break 100 bricks
Use a powerup
Used a powerup 5 times
Used a powerup 20 times
Completed a level
Completed 5 levels
Completed 10 levels
Completed 20 levels
Defeated a boss
Defeated 5 bosses
Defeated 10 bosses
Break 1000 Bricks
Used a powerup 1000 times
Defeated 100 Invaders
Defeated 500 Invaders
Defeated 1000 Invaders
Completed Standard Campaign
Completed Doodle Campaign
Completed Retro Campaign