Blizzard has finally confirmed “Reaper of Souls” the Act V of Diablo 3. There would be new cap level as well as a new class - The Crusader. Angel of Death Malthael become the final boss of the Expansion. You can get more information at Reaper of Souls Page.
New Class - The Crusader: This is a middle distance melee class. You have to buy the expansion to play this new class and Act V. But you can still enjoy the paragon 2.0 and items 2.0 without buying the expansion. From the skills, you can find that actually it is the combination of Monk, Barbarian and Wizard. I bet, it would be the strongest class ever.
New Boss - Angel of Malthael: I think the image of Malthael is scarier than other monsters who is the perfect choice to be the final boss of Act V.
New Level Cap: You would not stop at the level 60. Now the cap would be 70.
New Game Mode: Loot Runs and Nephalem Trials.