Here is the full list of all 12 Osmos (GFWL) achievements worth 200 gamerscore.
Completed five levels in any Forever zone!
Completed three levels in each Force Forever zone!
Completed three levels in each Sentient Forever zone!
Completed three levels in each Ambient Forever zone!
System collapse in level F2-3 achieved!
Game completed!
All Ambient zones completed!
All Force zones completed!
All Sentient zones completed!
All zones unlocked!
All tutorial zones completed!