Overall this was a very competent game, and a good entry in the stealth game genre. The powers all felt good, were presented well, and made the player feel powerful and deadly.
My biggest problem with the title was the mixed messages it sent about how powerful and deadly you should feel. For example, you're constantly reminded that you don't have to use violence, and can use stealth instead. The missions themselves even have ways to "eliminate" your targets without killing them (usually presented via some not-too-subtle dialog between npcs who are strategically placed in a bottleneck so you can't miss them). There are, indeed, achievements for completing missions without killing or being seen by anyone.
Strictly speaking it's not a failure case that you get spotted, get in a brief fight, and use your badassery to beat up on some Overseers. And yet you're made to feel as if this is a loss condition, and a reload is the only solution. To make matters worse, the only alert you receive if the character who discovers you is off screen is a musical stinger, letting you know the gig is up. Should that coincide with other noises, or should you just miss that, and move on with the level, there is no way to check that you have in fact not been discovered this mission. No, for example, secondary objective like "Don't be seen by anybody" that gets marked as failed if you are seen.
Several of the powers you can unlock, and most the workshop upgrades, are similarly geared towards the violent actions you can take. It seems pointless to take a power that lets me get rid of dead bodies if I'm being told to not leave any dead bodies in the first place.
And so I'm torn. The game is constantly steering me to be both a crazy murderous ninja, and a sneaky pacifist who just wants everyone to get along. Arkane may have done this on purpose, in an effort to lend "weight" to your decisions, but I think it leads to a confusing message about what the game should even be about.