You can always choose not to kill. Dishonored – as perhaps befits a game designed by the men who made Deus Ex and Arx Fatalis – is an assassin game where you don't have to assassinate anyone. Silence, shadow, occlusion and distance protect you from discovery as you stalk side streets and rooftops, and by exploring all your options you can even find ways to eliminate your target without actually killing them.
The developers estimate only one per cent of players will want to take this path, but they evidently care about that one per cent, allowing them to save anywhere – even on console – so they can try to preserve that invisibility by recalling earlier states.
Arkane clearly wants you to experiment, too, allowing for partial failure all over the place. In our demo, Corvo sneaks into the lawyer's home and makes it to his office – lurking in shadows, peering through keyholes and waiting for guards to pause in front of paintings or warm their hands by fireplaces to sneak past on the way – and eventually confronts and kills him in a blaze of magical abilities. But if you do alert the lawyer, you can continue – he'll cower somewhere, or run away, and that will change the way the mission unfolds but won't stop you from succeeding in it.
It turns out the rats in Arkane's Dishonored serve a much larger purpose than you might initially expect. When the appropriate powers are acquired it's possible to spawn rats into a fight to distract and even strip the skin from aggressors. You can possess them as well, taking the form of a rat to slip through small sewer grates and around enemies to reach a destination in safety.
If the idea of utilizing rats as a method of attack and exploration is entirely unpalatable, it seems you can ignore it entirely in Dishonored. It's a stealth action game that blends the multi-path exploration elements of Deus Ex with the combat variety of BioShock, all set in a fictional world designed by Viktor Antonov of Half-Life 2 fame. The mission-based excursions are isolated – this isn't an open world game – but within each space it's apparent there's plenty to do aside from the main quest. You can explore to find items, coins and more to power up your character and select skills, get side quests from NPCs and pick up blueprints to more skillfully interact with pieces of technology. All your actions of senseless violence or deadly precision are fed into a chaos system that will eventually affect how the game progresses. Arkane stresses this isn't a system of good or evil – the game isn't morally judging you for what you do – but the chaos rating will stick with you throughout the play experience and potentially alter the path of the story.