A lot of fans were shocked when Superman snapped Zod's neck at the end of Man of Steel. You could see on Superman's face though that it wasn't an easy choice for him to make. We really didn't get a chance to see how that affected him in the first movie. But Zack Snyder recently hinted that we'll see the ramifications of his lethal action in the sequel Batman Vs. Superman.
At a fan event Snyder addressed the issue of killing Zod saying,
"It's a real world problem. I think the effect on Superman, it is a deeply difficult decision for him to make."
The director then went on to say we might see the repercussions of that in the sequel,
"It's not a thing that he takes lightly, and you can see it affects him pretty profoundly. And maybe we'll see the repercussions of that in the next film. How that's affected him, making that decision… Maybe."
Of course we will see how it affects him! It would irresponsible for Snyder not to address it. I have no idea why Snyder needs to act all coy about it. The director goes on discuss the "unwritten rule" about Superman not killing people,
"Well, what's funny about that rule is that it exists in the movies. But it doesn't really exist in the comic books. He's killed Zod a couple times in the comic books. Killing General Zod is a practical solution to the problem. He wouldn't let his personal aversion to killing cost the lives of an entire planet or those little kids, that little family. So if he had said, 'I'm just morally opposed to killing so I guess I have to let him kill those people.' Those are the dilemmas. We set that up directly so there would be no solution other than that solution."
It really shouldn't have been such a controversial issue. Superman had to do what he had to do, and the decision will, in a way, help shape him into the superhero that the world needs.