The Crusader will be joining the fight against demons, with an all-new Act, higher level-cap, endgame options and a treasure imp's ransom of loot. It's set around angel Malthael.
The angle of death, Malthael, has taken the black soulstone for himself and is now reaping souls from the poor people of Sanctuary, and even turning them into thralls.
Westmarch is the new destination for Reaper of Souls, which is a sprawling city environment with secrets to plunder and Death Orbs to, maybe, avoid. The Crusader is similar to Diablo II's Paladin in that they're holy knights. Blizzard describe them as a "war machine made human. The Crusader packs skills like shield bash and a deadly technique called Falling Sword, which basically turns the Crusader into a bolt of lightning crashing down from the heavens."
Blizzard are also applying what they call 'Loot 2.0'. This new loot drop system is "smart" as more items will be geared (literally) toward your current class. Overall loot levels however will be reduced so that players aren't warmed with junk all the time and forced to pack mule it back to town.
More details continue to reveal.