I started playing yesterday. I'm intrigued by the beautiful environment and the story. However I was put off by the rather abrupt introduction of violent gameplay. I mean, I'm not sure what I was expecting - I knew combat would be central to the game. I guess what bothered me is I felt like I had no choice and the game was going to force me to slaughter what seemed like innocent people. I actually decided to try running past enemies but ultimately had to fight.
It's not the violence itself that bothers me. It's that I didn't feel I had enough information about Booker or Columbia to understand the reason why I had to start killing. Mostly I've rationalized it by telling myself the citizenry is mostly fanatical, that they've been repeatedly told to look out for the false prophet, and that the player as Booker must react first in self defense. I found it unsettling for the first couple hours of play, though I've adjusted now.
Perhaps I'm too comfortable with the stealth components of recent games like Deus Ex: Human Revolution and Dishonored.