The writing of many Marvel movies is questionionable and often terrible, yet they great amazing reviews. Why is that? They don't get 56%. How did this get so low? It's a good question.
We see the Avengers cause tremendous collateral damage, Tony Stark even invents Ultron, almost causing the end of the world. Yet seeing Superman kill one guy is bad? Just accept that he is a new take on the character. The more I thought about it, the more I saw how it fits in with the themes in the movie, and especially with the follow up films (Bruce witnessing the Zod battle from below and giving the human response in the next film), how it fits in with Snyder's overall vision.
I get the argument that it's not the old Superman. But it's not going for that, it is a more emotional take, more in conflict with his role on Earth, a more complex and self-doubting take. Really the shocking thing in that final scene is not that Superman kills Zod, but that it impacts Superman in such a strong way, he cries out. All movie long he is searching for a morality, a moral center to call his own. Why this moment is shocking is not just the violence of the act (which is what critics dwelt on) but that Superman is killing one of the few remaining members of his home planet. In fighting Zod, he is almost, in a way, fighting his Kryptonian past. And while it's easy to call the terraforming machine a lazy laser-in-the-sky, in an interplanetary way it makes sense, they want to turn this into the new Krypton. The symbolism of Superman fighting against all this couldn't be more clear, he is fighting against his past. In order to live on Earth he is paradoxically having to kill a potential Krypton2. There is something very tragic and personal in that, and Snyder approaches it with the proper amount of operatic grandeur.
I don't know, I felt like it was really honest to who Superman is, even if it was a darker take. Regardless of what you think of the film, you have to admit Cavill is a great Superman.