Looking back to the move 5 days after, I have to say I really loved the beginning. More time show on Krypton than I recall in any of the other movies. As far as Superman's mom not getting all crazy after seeing her husband killed, I believe that was on purpose. She had given hope of living and just wanted to keep it together so Cal had a chance of living in a new world.
The flashback scenes worked for me. Got to see how Superman got his mindset over the years. I go agree I thought it was odd in the school that all the kids were behind the teacher as she was trying to talk to Superman, but really it was not a huge distraction. It's a super hero movie and still way better than others I have seen.
The action scenes although long seem to fade more from my memory as days go by since I have seen the movie. So it obviously wasn't too bad where it would make me dislike the movie.
The biggest plus for me for the movie was the absence of Jimmy Olson. Hated that character in the show, the comics and other movies. Weak, annoying character that would take up space better occupied by someone else.