The Dishonored Website now offers the debut trailer from Dishonored, a mostly cinematic look at Arkane Studios' upcoming steampunk shooter (thanks Chris). The post about this on the Bethesda Blog offers an updated description of the game:

Dishonored casts you as a supernatural assassin driven by revenge. You are the once-trusted bodyguard of the beloved Empress. Framed for her murder, you become an infamous assassin, known only by the disturbing mask that has become your calling card. In a time of uncertainty, when the city is being besieged by plague and ruled by an oppressive government armed with strange technologies, dark forces conspire to bestow upon you abilities beyond those of any common man.

In Dishonored, creatively eliminate your targets with the flexible combat system as you combine the numerous supernatural abilities, weapons and unusual gadgets at your disposal. Pursue your enemies under the cover of darkness or ruthlessly attack them head on with weapons drawn. The outcome of each mission plays out based on the choices you make.