I just did a lot of thinking on this issue and here are my two cents on it:
Having Superman kill Zod is brilliant.
No really, if it plays out as described, I think that's a great climax to this movie. Because think about it, this is a story of Kal-El trying to find his place in the world, where loneliness and isolation are key themes in the film, as he struggles to fit in with the rest of humanity. But then it turns out that there were actually survivors from Krypton and now Kal's entire world is turned upside down. He has to make a decision to either side with his people, or defend Earth. At the end he kills the only other (assuming the rest of Zod's henchmen are dead at the time) surviving Kryptonian, in order to save humanity who've sheltered him his whole life. The weight of that decision has got to be so overwhelming to him, it's indescribable.
I'm sorry but an ending like this fits so well with the theme of this movie. Some of you may not like it, and that's understandable, but I really think people need to give it a chance here. God forbid we see the guardian of humanity make extremely difficult decisions and express heavy emotions afterwards.