Blizzard Entertainment just announced it is re-creating the original Diablo in Diablo III, with 16 levels of underground horror for players to conquer, including facing off against all 4 Prime Evils again! As expected, the new Necromancer class is announced for a 2017 launch, but this new class will be part of a paid downloadable content (DLC). There will be 2 new maps arriving as well in Diablo III.
Update: Blizzard has issued a takedown notice for all my BlizzCon videos except for big partners like IGN, so here are the videos from IGN.