Makenshi
Ahoy, ye salty dogs!

"Death, at last, shall spread its wings over all…"
A presence more sinister than any demon hangs over Sanctuary….
It watched from the shadows as a hero of nephalem lineage struck down Diablo, the Prime Evil, and trapped the demon lord within the Black Soulstone.
It waited in silence as the mortal armies of Sanctuary crushed the leaderless remnants of the Burning Hells and scattered them into the stinging winds of Kehjistan.
Now, as hope springs anew, its long vigil has ended.
Shrouded in mystery and imbued with a power as ancient as the universe itself, it comes to the war-torn world of Sanctuary. It cannot be stopped. There is no escape.
In its wake, only death will remain.
[youtube]http://www.youtube.com/watch?v=Cb7QJwQ58T0[/youtube]
[youtube]http://www.youtube.com/watch?v=zGp5dkJdi0w[/youtube]
The next chapter in Sanctuary&'s epic saga has been unveiled. Prepare to take on Death itself in Diablo III's upcoming expansion set: Reaper of Souls.
In Reaper of Souls, players will explore haunting new environments and face down fearsome new enemies within and beyond the world of Sanctuary as they seek to unlock the mysteries of Malthael, the Angel of Death.
Stalwart adventurers can choose to continue their journey as one of five existing heroes—the Barbarian, Demon Hunter, Monk, Witch Doctor, or Wizard—or adopt the mantle of a new class: the Crusader, a fierce melee warrior whose command of the battlefield is matched only by his unwavering conviction.

Advance through additional levels of supremacy, mastering bold new powers of raw, demon-slaying potential along the way. Customize your strengths with an improved Paragon system. Battle your way through newly randomized 3D maps and epic new quests in Act V. And test your mettle in all-new game modes—including Loot Runs and Nephalem Trials—designed to provide players with a highly replayable (and highly rewarding) end-game experience.

For more information, check out the official press release and be sure to visit the new Diablo III: Reaper of Souls web page for feature details, screenshots, concept art, gameplay teaser trailer, and more.
Sources:
http://us.battle.net/d3/en/blog/10648023/diablo®-iii-reaper-of-souls™-revealed-8-21-2013#best
http://www.diablofans.com/news/1978-diablo-iii-reaper-of-souls-revealed/
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When I saw the news that a shield specialist in the vein of the warrior (D1) and paladin (D2) was announced, this was my reaction (forgive me if gifs are not allowed, it's been years since I read the rules and I don't remember this specifically; just tell me and I'll remove it):

Anyway, in the Diablo Fans link there is a recap explaining all the new stuff (features etc etc etc), here is a snip (is this the right word? snip?):
New Class - The Crusader
Inspired by the Paladin.
Focuses on Shields. Uses Flails as weapons.
Mid-range melee character.
Uses the resource "Wrath"
New Feature - Loot Runs
15-20 minute completely random dungeons!
Random weather!
Random enemies!
Random boss!
Multitiered (severa levels deep)!
The Mystic
Can Transmogrify items, so you don't have to sacrifice looks for power.
Item Enchanting - allows to reroll one of the affixes on a rare/legendary item.
New Level Cap - 70
Every class gets new Skills and Runes
Which means a fresh economy and new power-cap as well
New Act
Featuring what looks like Westmarch, with lots of graveyards and other fun places! (I read somewhere in there and in the official site that the Pandemonium Fortress is also in the expansion)
Major Paragon Changes
Is now Account wide.
No longer has a cap
Seems to have Stat Allocation tied to it
“Changes to the game systems will come in a patch preceeding the release of the expansion – they will be available to all players, including the ones that don’t have the expansion (of course for free).”[/img]