Minecraft wiki entry for Development_versions, associated text: Rewrite of the achievement system.
Are now per world/server
Added 744 new objective criteria
New achievements: Repopulation, Adventuring Time, The Beginning?, The Beginning., and Beaconator.
Achievements screen can now be zoomed in and out using the mouse wheel.
Achievements don't appear on the achievements screen if more than five achievements need to be achieved first.
Example: "DIAMONDS!" doesn't appear until "Getting Wood" is achieved.