The upcoming Diablo III patch will have a few updates to items and Greater Rifts, but the big thing is the recreation of Diablo 1 for the 20th anniversary of the series. It's not just the levels done Diablo III style, but there are a lot of small little things in there to make it a great experience.
When you enter this world, your movement's locked to eight directions and the graphics have a more pixelated look to it. The sound has been made to mimic the classic even more and UI changes a bit to look more like the original. The team even redid the Butcher model to be more like the first game, rather than reusing the Butcher from Diablo III.
You'll get all 16 levels of Diablo 1 to play with. Unfortunately, this dungeon will only be available for January, which I think is a bad decision. They should have it permanently available rather than just one month. Let's hope Blizzard changes its mind and allows for the dungeon to be available at any time.
Yeah, I'm going to have to reinstall Diablo III and try this out before they take it off the servers.