At Gamescon 2013, Blizzard has officially announced their expansion to Diablo III, called Reaper of Souls. Accompanying the announcement is a cinematic trailer to introduce the game, as well as a gameplay trailer to show off the new class, enemies, and environments.
This cinematic, like all of Blizzard's, is staggeringly gorgeous. It picks up where the original game left off--the imprisonment of Diablo in the black soulstone. The council of archangels (in their oh-so-infinite wisdom), decide to just...you know...hide it somewhere. It apparently cannot be destroyed, and it's too evil to put into storage in heaven, so they just take it somewhere and hide it. This plan, not surprisingly, fails spectacularly. Not moments after Tyrael places the soulstone into his super secret chamber, Malthael, the archangel of Wisdom and apparently Death now, shows up and steals it after killing everything (in an absolutely beautifully rendered way).
Also released was this gameplay teaser. We get to see the new class, the Crusader, in action as he battles through hordes of Malthael's undead armies. He's obviously the spiritual successor of Diablo II's Paladin, using holy attacks and protective auras.
The expansion will contain, well, what you might expect it to. A new Act with a new story, new environments, and new enemies. All of the existing classes will get some new skills and abilities. Blizzard will also be retooling some core aspects of the game, especially regarding loot. They'll change the distribution so that item drops will be fewer but more powerful, including more creative legendary items. The previously scrapped Mystic artisan will be returning to help customize your character and loot. The level cap will be raised from 60 to 70, and the Paragon system will make character customization more rewarding.
Notably, a lot of these changes reflect what fans have been asking for since the game's release, so it looks like Blizzard has been figuring out how to implement these fan suggestions.
The expansion does not yet have a release date, but look for it next year. Until then, you can get excited about Diablo III's console release this September.