CodeBlack, you're completely missing Aesirs points.
I'm just going to take one thing you said to show you what I mean.
"hell, Goku being in high school defies the premise of Dragonball entirely"
You're saying that since Goku was a child in dragonball and this Goku is older it should not be called Dragonaball. Yet, in DBZ Goku was a adult so this film should not be called DBZ either correct? Do you see how ridiculous that is? Who cares how old he is?
You can't fit 100's of hours of animation into a single film. It's not realistic to expect a exact re-telling of the same stories that you are already familiar with. Nor is it necessary. As long as they keep the core elements of the DB universe it's ok.
Not age, setting.
Goku travelling around the world, exploring, meeting people and going on adventures is a huge part of DB's setting. Him going to a high school and defending a town from evil is less of a Dragonball movie and more like a teen hero movie with a Dragonball twist.
Ok, for that last paragraph. I really hate repeating myself, but for the third time. Every film made take some liberties. Every single one. Everyone knows that. The difference between a good adaptation and a bad adaptation is how much they mess with the premise itself.