Burton's Batman took place in such a heightened, operatic, comic book world that I've always had a hard time taking those killings very seriously myself. The villains in that movie might as well have been cartoon characters.
Regardless of them being comic characters, I remember being taken aback that Batman killed outright in those movies. Specifically, I remember the bomb in the plant and throwing the guy to his death in the clock tower. It wasn't the comic book Batman that I knew, but I enjoyed the movie any way for what it was. Two hours of Kim Bassinger screaming.

Well this is the same Batman who is also going to appear in the following Justice League, so I doubt Snyder or WB would want to make him too dark or psychotic in this movie.
And I'm guessing the gun turrets are used more for blowing up walls and obstacles in his path, or shooting out the tires on cars and trucks. Just like the guns we saw on the Tumbler or Batpod. I really doubt Batman is going to be simply mowing criminals on the street down with it.
But it would be an interesting take for the Batman to go after Superman for making a mess of Metropolis only to realize his own mistakes. The two heroes draw inspiration from each other and grow spiritually before the end of the film....
Oh, this is 2014--sorry, forget that suggestion...