Played a little bit of Dishonored while the lines were still short. Here's what I saw:
-Game is mission-based
-Lots of abilities/powers [including summoning a hoard of mice to attack guards]
-You can summon a hoard of mice to attack guards
-Crossbow, pistol, knife were among the available weapons
-Lots of routes to use in levels, very vertical as well
-Lots of stuff to pick up [including things that just give you money]
It really does feel like a spiritual successor to the Thief series.