Dishonored: Stealth is Optional, Killings Will Carry Weight
Stealth in Dishonored is entirely optional, but not being a murderous bastard in the game will give you a nicer ending.
Dishonored is being touted as a stealth game with action elements (or an action game with stealth elements), but the developers want you to know that the game's stealth elements will not be actively forced upon the player.
According to the developers, you'll be able to make your way through the entirety of the game cloaked in shadow, or simply blast your way through with the aid of weapons, mechanical gadgets, and what passes as magic in Dishonored's world.
The reason for the optionality of stealth, says Arkane, is because they don't want failing stealth to be a fail state, and because they want players to be able to express themselves.
"The funny thing is that we do consider that Dishonored is a stealth game because stealth is very important, but it’s not enforced. You could totally play without stealth and that’s important to us because it’s not like you play a mission, and then as soon as you get discovered you fail the mission," said Raf Colantonio in an interview on VG247.
"For us the stealth element should be in every game as part of the simulation. If you play like Far Cry 3 or S.T.A.L.K.E.R. you know – any game that gives a sense of simulation – I think stealth should be in their systems."
Likewise, non-lethality is equally important as stealth because the developers want your killings to carry weight. To that end, keeping the kills minimal will allow you to get a "brighter" ending to the game's story.