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