-A new Crusader class, wears heavy armor as a tank, buffs/debuffs friends and enemies, not unlike Diablo II's Paladin
Reaper of Souls will officially by Act V of Diablo III
-Level cap raised to 70
-Paragon level cap removed
-All classes will get new spells as they progress to level 70
-Something called a "multilevel Legendary item"
-Substantial updates to the loot experience, "Loot 2.0" as named by Blizzard -- you're more likely to pick up items tailored to your current class
-Overall loot reduced, not picking up as many items not needed by your current class
-New Crafter: Mystic -- re-roll stats on items, gives chance to create better gear
-Two new endgame modes/activities: loot runs and Nephalem Trials