A comment I read on io9, that I loved, was someone who said "Man of Steel isn't Superman: Year One, it's Superman: Day One." It's true, too. At best, this is Superman's first week on the job. That's why I think the movie's so, shall we say, "not fun," at times. It's a journey of self-discovery, and it's not a Superman movie; it's the story of how Clark Kent became Superman. I think the whole point of that film was that he wasn't the Superman we know. That's where the realism comes into play. I think we'll get the big, blue boyscout, but, unlike the books, I think the point they're trying to make is that he's got to grow into that character; he can't just be born that way I think that's where Zod's death comes into play. He's seen firsthand how killing feels, and he never wants to do it again; we see how that crippled him, emotionally, even though he was perfectly justified, considering the situation. With that in mind, I'm hoping and praying that Snyder has the vision to see that through, and to use that in this story. To me, Zod's death is the perfect in for Batman, which is why I'm against the folks who say that he's just there to make more money.
The circumstances of Zod's death don't matter; all that would matter, to someone as morally stagnant as Batman, is that, with the right amount of pressure applied, Superman is capable of taking life, and that makes him one hundred times more dangerous in Batman's eyes. With that in mind, we start to see that Superman that we know at the end of Man of Steel; Clark's wearing his glasses and working at the Planet, and Superman's on his way to becoming the hero that we all know. Man of Steel isn't the whole story, it's just Act One.