Parts of this movie felt like they belonged to a very good movie, which this was decidedly not.
It was so disappointing because there were some great things about it. The acting was uniformly good, especially Amy Adams. I liked the take on Clark as a drifter running away from himself and not yet ready to accept his dual identity. I liked the Jesus allegory, which has always been there with this character but never as strongly as in this movie. I liked Clark's divided loyalties and how no matter his choice, something had to be lost for something to be gained. I liked that parts of it seemed to really aspire to be more than the usual superhero movie.
Unfortunately, it was all undone by the same things that undo lots of big action movies - inane, too-long fight scenes; superfluous VFX-for-VFX-sake setpieces; muddy, poorly-explained movie science with no internal logic, and a script that seemed to be cobbled together in editorial after the movie was shot. It feels like someone had a vision for the good version of this movie and lost a power struggle. Not sure it would have been Snyder based on his history, but it might have been Nolan or Goyer.
I would have shortened the Krypton portion of the movie. Even though it was good, it was more than we needed. I would have told the story in more of a chronological order; I appreciate time shifting when it's warranted, but the flashbacks here served no narrative purpose. I think the story of Mr. Kent's and Clark's relationship and its effect on Clark's behaviors and attitudes would have been better served to be told early in the movie so his evolution hits a better emotional beat later on. I would have found a better way to serve the story than to have Jor-El pull an Obi-Wan, which felt cheap and hacky. I would have eliminated a lot of the fighting; it was so redundant I wanted to scream. The movie needed action and fighting of course, but not to the point of exhaustion. I wanted an acknowledgement of the folly of Superman and Zod physically fighting and I would have had a victory decided on cunning instead; it would have allowed the human half of Clark to be the reason for his victory, which would have been immensely more satisfying and appropriate. Certainly more satisfying than the utterly ridiculous way their battle was decided.
What was good about the movie lost to what was bad about it. It was like a fine dining restaurant that puts hamburgers on the menu. It wussed out because it didn't trust itself.