You get the same types of choices that you get in the first two games, but it’s really streamlined. And you can absolutely murder/spare people as you see fit because it doesn’t really affect the outcome. There is an achievement for clearing a single level without killing anyone, but not one for the whole game.
I didn’t even realize there wasn’t a chaos system until I finished the first level. I still played my usual way on that first playthrough, though (ghost/clean hands). On the second run I murdered everyone. Third run was the Original Game+ (where you get to use some of Corvo’s and Emily’s powers instead of your own)… that one was actually the hardest because Billie’s powers are honestly better, at least in this one.
The only thing I’ve never really done in these games is go with the combat-- I’m purely stealth. I know the combat is amazing and completely open-ended, but I honestly suck at it.