Full list of all 12 Orcs Must Die! achievements worth 200 gamerscore. It takes around 15-20 hours to unlock all of the achievements on Xbox 360.
Kill 1,000 orcs
Kill 30,000 orcs
Complete Act 1
Complete Act 2
Complete Act 3
Complete the campaign on Nightmare mode
Earn 5 skulls on every level on War Mage difficulty
Win a level with 1 rift point left
Get 50 kills with the rolling log in one level
Get 50 kills with explosive barrels on one level
Gib more than 200 enemies on one level
Get 20 chandelier kills in one level