Dishonored is about tools. You're the bodyguard of a murdered empress – nice job, by the way – and you've been framed for her death. So you're trained in combat, but even you can't hack through everyone you'll face in this strange and tumultuous city. You're going to have to rely on your tools, conventional and otherwise.
Dagger, crossbow, traps. The basics are effective, but they're not tools of brute force: the perfect application of each means using stealth or other trickery to get the jump on people. A single guard facing the wrong way can be silently backstabbed, but if that situation doesn't present itself, Dishonored gives you the powers to engineer it.
'Blink'. Dash forwards in an instant, skipping all the space between you and your destination. A blinked-into opponent is staggered by the force, and Dishonored is littered with collapsing scaffolds and other grisly fates for the stumbling victim. Developers Arkane have proven their knack for environmental misfortune with Dark Messiah of Might and Magic.
'Pause'. Something of a step up from the traditional Bullet Time. Time is frozen for everything except you and the things you interact with: you can load and fire your crossbow, but the bolts won't go beyond its prod until time flows again.
'Vanish'. Not yourself, but a body. You could drag them around to a hiding place, but if you really want to be sure the corpse won't tip anyone off, quietly vaporise it with your supernatural powers.
'Possession'. A risky gambit, this is where you become someone or something else. Man or beast are equally viable candidates, but if you're going to jump into a rat, be aware that if it dies while you're in there, so do you. You're actually in your host, in some gruesome sense.
There are more tools, but the combinations of these alone are what really make Dishonored stand out. The dagger lets you backstab, but it's the other tools that can put you in position to do so: blink past your enemy to get behind them, pause time and stroll to the best ambush spot, or possess one of their friends to get them when their guard is down.
Games that allow this intricate play are sometimes called immersive sims: a rather vague-sounding subgenre that covers intricate games like Thief, Deus Ex and System Shock. They're all about tools, a wide selection of abilities that follow consistent rules the player can find creative ways to exploit.
A lot of those great games didn't sell that well, so it was a rather underserved genre for years. But since BioShock's massive success, it's been slowly mounting a resurgence. Between Syndicate, BioShock Infinite and now Dishonored, 2012 could be the year the immersive sim rides again.