At BlizzCon 2016, Blizzard announced that it's recreating the first Diablo game inside Diablo III in an "Anniversary Dungeon".
Head to Old Tristram in Adventure Mode during the month of January to discover a portal where you can explore a Diablo III recreation of the events that transpired in the original Diablo. Filled with iconic enemies, familiar faces, and some old-school items, this event is a nostalgia-packed adventure down memory lane. Transmogrification rewards, achievements, and a few extra surprises await those brave enough to plumb the depths below Tristram.
This will be a limited time event, recurring in January every year going forward. The dungeon will be sixteen levels deep and feature returning bosses like The Butcher, The Skeleton King, Lazarus and obviously Diablo himself. There'll be a distinct retro style to it, both in regards to visuals (there will be special audio and visual filters) and gameplay (you'll only be able to move in eight directions, just like in the old game, for instance). Even Diablo III's User Interface (UI) will be changed to something more closely resembling the one in the original Diablo.
Moreover, the rumored Necromancer class has been confirmed and fully detailed. With both male and female characters available, the Necromancer is included in the "Rise of the Necromancer" pack alongside two additional character slots, two additional stash tabs and a pet. The pack won't be free, of course, though no price has been announced yet; Blizzard did say players can expect it in the second half of 2017, though. You can read a lot more on the Necromancer, including skill/ability samples, in the official blog post.
There's more, as Blizzard also talked about two new upcoming zones, The Shrouded Moors and the Temple of the Firstborn. These will be available in Adventure mode next year, free of charge.
Challenge Rifts, which will provide a completely even ground for all characters to compete via leaderboards, are also expected to hit in 2017. Finally, the Armory equipment manager will let you save up to five loadouts per character and a new interface should make crafting a lot simpler, given that materials won't take up any more space in the inventory.