Here is the full list of all 28 Peggle 2 achievements worth 400 gamerscore. It takes around 25-30 hours to unlock all of the achievements on Xbox 360.
Complete every level in the Peggle Institute
Complete every trial in the Peggle Institute
Complete every level in Mountain Highs
Complete every trial in Mountain Highs
Complete every level in Winter Blunderland
Complete every trial in Winter Blunderland
Complete every level in Gnorman's Gneighborhood
Complete every trial in Gnorman's Gneighborhood
Complete every level in Gravely Grove
Complete every trial in Gravely Grove
Complete every Celestial Realm level
Complete every Celestial Realm trial
Complete 30 Optional Objectives
Complete 60 Optional Objectives
Complete 90 Optional Objectives
Complete 120 Optional Objectives
Complete 150 Optional Objectives
Complete 180 Optional Objectives
Win a level with at least 12 balls left (Except Trials)
Earn 3 free balls on one shot (Except Trials)
Get 75,000 styleshot points in a shot (Except Trials)
Win a level with the cool clear style shot (Except Trials)
Hit 10,000 blue pegs
Hit 5000 orange pegs
Hit 300 green pegs
Clear all orange pegs in a level
Beat your first ace score
Clear all pegs in a level