As for the many atrocious problems with the movie adaptation, one of the worst in my opinion is the changing of the rules of firebending. And the general weakness of all the benders except for anag kinda... we must make show that a proper movie will show bending as the creators intended it to be. NO Having to have torches for fire! NO Having to have a dozen earthbenders dance in order to lift one stupid rock!
And the actual progression of bending in general needs to be shown. No katara being able to kick everyone's butt at day one. It also imperative that each bending ability be correctly attached to each different fighting style and emotions represented by each element.
All of these are important things that need to be fixed for a new movie series.