I think what makes him killing Zod at least "work" as that it seemed he really had no other choice and the way he broke down in anguish after doing it.
I also think the destruction inflicted on Metropolis in this movie is way over the top considering several blocks of it was pretty much vaporized into oblivion. After The Avengers there was talk about the amount of damage done to NYC in terms of dollars (I don't recall it, but while it was steep it was on par with most natural disasters) here? A good chuck of Metropolis is LEVELED, gone, and then there's a lot of secondary damage from the fight between Zod and Superman (which it would've been nice that if instead of seeing buildings collapse killing countless people we see Superman do things like weld back support columns and stuff to prevent a building collapse.
Again, it goes back to how much the MCU tried to ground itself in "a" reality and not make things too far over the top. Here? Metropolis is highly destroyed, countless people are no doubt dead and as a result of the terraforming device Earth's entire gravitational pull has been slightly altered.