I saw the movie recently. The first thing I'd like to say is that the special effects were amazing. The character designs were both faithful to the original book, and perfectly believable. Very well done there.
Now, regarding the themes, I have three things the story's themes could be. They were either
a) extremely deep hidden meanings, too profound for my mind
b) a bunch of random talk which was meant to sound profound, but was really meaningless
c) there is no true meaning, but the writers wanted to leave that open, for the audience to take their own themes
If my third hypothesis is the case, then I shall say that I truly did find meaning in the plot with Carol's getting so mad at the realization that Max wasn't some omnipotent being. I know too well the enraging disappointment of finding that ones' parents can't solve any problem. This movie helped me see it from a different view.
Though I thought that teacher was a bit of a jerk. Really, who tells children his age that the world will end? If he doesn't think he'll contribute to preteen depression, I don't know what his problem is. Him and Judith, Judith was kind of a jerk too.
And poor Douglas! I felt sorry for him seeing him with a stick where his hand was. That was pretty nasty of Carol to do that to his best friend.
Though I must say Alexander was my favourite. I think I'm most like him.