Tyranny is an upcoming RPG from Obsidian and Paradox that has a simple, but rather effective premise behind it: What happens with the world if the bad guys prevail in that final, cataclysmic showdown between good and evil?
If you're looking for a detailed answer, I'm afraid you won't find one until Tyranny finally releases at some point in 2016, but if its the gameplay you're curious about, Obsidian has you covered as they have recently done a ~40 minute stream showcasing just that. Here's the Youtube version of the footage, recorded by Gamestation:
While the gameplay is still a bit rough around the edges, I can see great potential in Tyranny, though that shouldn't come as much of a surprise given how stellar Obsidian's latest RPG, Pillars of Eternity, ended up being. How the story is going to be handled, however, we know very little of, but that's one aspect of Tyranny I have no doubts Obsidian will be able to nail down perfectly, even without Chris Avellone's guiding hand behind it all.
If you would like to learn more about Tyranny, its lore and its characters, I would recommend you head over to the official website. It'll get you clued in pretty quickly.