Dark Vision kinda ruins the game, in my opinion. I would avoid that power if I were you. It's a lot more intense and immersive without Dark Vision. DV makes the game... uh, too gamey? for my taste. DV neuters the appeal of sneaking around, in my opinion. I want the thrill of trying to remember where each guard is going, and doing trial and error runs, I don't want a highlighted easy mode.
If you like challenge, Dishonored isn't going to satisfy a hankering for a challenging game. Even on hard, it's not tough, but the power fantasy and trying to make each encounter as varied as possible by trying new combinations of items and powers, can keep it very fun and fresh. At least, for one playthrough. I didn't find it remarkable enough to be worth much more than maybe one slow, deliberate playthrough and a second crazy, madman kill everything playthrough (which goes really quickly). I'm hoping the new DLC is good--the challenge maps got old pretty fast, game is too clunky for fun score attacking, or maybe it was just me.
I would suggest not doing a full stealth, no kills run your first time, nor a full on madman. I think the game plays best when you mostly sneak, but have to deal with getting caught, or sometimes feel compelled to brutally dispose of some particularly nasty people. In other words, use all your items and powers and don't abuse save scumming. The game is best when you're constantly having to improvise.
It is very true that the game isn't very good outside of aesthetics (technically speaking, it is a bit ugly), world building and the gameplay. Its story, characters and some of its lore are poor and entirely forgettable. If you need a good story to get you through a game, look elsewhere. This game's Pros are all in the gameplay column. The world is interesting, but mostly nothing in the world is interesting, if that makes sense, beyond the "seeing what's around the next bend" factor.