they devoted about 2 minutes to an entire episode of the show which led to people who have never seen the series basically lost. the acting was terrible as well as the character casting (they left some people out even) and i know its probably hard to make it look real but the element bending was cheesy and retarded

also the story was so rushed you never got to enjoy a scene before it was over. and simply put it had no humor, though there is so much humor in the show. if you ever watched a m night shamalan movie you know how most of the characters almost stand wooden or talk very slow or something. That is the opposite of what you want to see in a avatar movie. Plus the racism of casting katara and sokka as white actors hurt the show. And people were mad the kyoshi warriors were not in the movie, including suki (sokka's love interest) And overall it didn't represent the show well

The acting was stupid.
They pronounced the main character's name as "uhng" instead of "Aang"
They got his tattoos wrong.
Zuko is supposed to have an epic face-scar.
The characters in general in the movie looked nothing like the ones in the TV series.
They had to do a little faggy dance to use bending, while in the TV show, bending was based on fighting techniques.