Wizards usually makes these announcements with a preview image (seen above) and what we can gather from that information. The thing that makes me most excited about the announcement is that Richard Garfield will be on the design team. Richard Garfield is the man who created the game of Magic: The Gathering (as well as other games such as RoboRally). He brings a very unique perspective to Magic design. The last time he was on a design team was for Ravnica, which is universally considered one of the high water marks for the game. He also has been on Tempest (personally my favorite set) as well as the Odyssey design team.
From the image, we can discern that there will be a heavy traditional horror theme. The woman in the image is widely considered to be planeswalker Liliana Vess. We see a Dracula looking vampire dead near her Thrown. I’m hoping for a more Eastern European flavor this time around. Think a Magic version of Castlevania. Either way, I’m really excited to see what they do in this world.