For starters, arms warriors and balance druids have been singled out as having seen big redesigns. Abilities have been moved, removed and redesigned. (Mortal Strike replaces Heroic Strike and Overpower is gone, for example.) The sections on balance druids and arms warriors are extensive. Survival Hunters also saw a new ability, Bear Trap, introduced. In addition, some changes were rolled back - paladins in particular see some roll back on previous changes.
For a full breakdown of the changes, you can go to the patch notes on the official site.