Corvo's creepy-ass mask gives you a good idea of the game's tone.
Like that other title, the plot revolves around assassination. And once again, the primary personal motivator is revenge; I suspect because narratively-speaking, it's actually quite difficult to 'justify' serial assassination with anything else, even if the people you are killing are objectively 'bad.' You play as Corvo, the framed bodyguard of a murdered empress, and you join the ranks of a rag-tag alliance trying to rescue her kidnapped daughter.
That story had the potential to be pretty interesting, but it is hamstrung by the decision to have a mute protagonist. The game tries it's hardest to give other characters personalities, but since you can only kill them or complete quests for them, they come across as road-bumps for your man-shaped car. I hope that one day this trend will go the way of Classical Dramatic Unities as well-meaning but primitive conventions that hold media back.
The world though! The world of Dishonored oozes character. The decor echoes The Combine from Half-Life as well as Victorian England and World War I Germany. As that recipe may suggest, it's almost relentlessly grim, but also a little bit mad. So far, I haven't fought any monsters that could described as Lovecraftian; there are no tentacles or squamous blobs to speak of, but the atmosphere of madness is here in spades. It's a dark world whose secrets are pulling it apart by the seams. And there is the Outsider to consider.
He may remind you of a darker version of Gaiman's Morpheus, what with his abraxael temperament and his pitch black eyes. Shortly after you join up with the rebels, he gives you the power to teleport short distances and the opportunity for more fearsome magic like possessing rats and people, slowing down time, blasting people with wind and summoning rats to devour bodies--dead or alive. He also gives you one of the coolest videogame tools I've ever received. A beating heart stuffed with clockwork that helps you find upgrades, and when prompted, whispers disquieting secrets about the world and the people in it. If you are making a storytelling game, seriously consider putting neat optional narration tools like that into it. At the very least, I will love you for it.
One of the coolest things about Dishonored is it's treatment of whales. Conceptually speaking, anyway. The actual treatment of in-game whales is appalling to modern sensibilities. They are tirelessly hunted so people can harvest ambergris, which is a real thing. Except, instead of being used to make perfume, it acts as a revolutionary, universally applicable and highly volatile energy source. It can power futuristic devices. It explodes if you shoot at it. The stuff is saturated with mystic power. And the same seems to be true of whales in general. You can collect charms and runes which are both carved from whale bones and used to purchase upgrades for your otherworldly powers. They are like currency for the Outsider.
It's one thing to invent a creature from whole cloth and say it's magical. Since you just made it up, how can it not be? It's another thing to take a known creature, especially one already fraught with significance and symbolism, exaggerating here and tweaking there to turn it into the driving force behind an entire world.
I think I've already sunk a good 15 hours into the game in my roundabout way, and so far I've only completed the first assassination mission. I'm not even attempting anything particularly fancy, like a no-kill or perfect stealth runthrough, though those options exist if you want to challenge yourself.
If you enjoyed Deus Ex: HR, Thief titles, or even BioShock, Dishonored is well-worth your ticks and cents.