Dishonored is a first person stealth, or action game depending on how you play it. The demo they played live took on a mission that they showed each path play out dramatically different. The game looks wonderful, smooth edges and dark colors with great lighting. Navigating the world is fluid. You can take soft cover and peek and never be seen. Your supernatural abilities let you zip from one place to another with ease. You can possess people and animals all while merging with them so you don't have to worry about your body being discovered. Guns are in your left hand and your switchblade knife in the right. The knife also helps represent when you are being stealthy or not, stealth when blade is facing behind you and not with the blade forwards.
The demo showed a successful run of stealth which looks to be a spectacular display of quick thinking and knowing the environment, which I fear you won't unless you play it a few times. The action approach is much faster but there's a lot of ability wheel switching which interrupts the game. Hopefully it doesn't end up being that way. Dishonored is not an open world game, it's linear in story but not how you obtain your objectives. Getting the job done is the primary goal, no matter how - so there brings some freedoms in each level.
Dishonored comes out October 9th, 2012.