I am a ATLA original fan. I've watched the cartoon hundreds of times over the years. Here is my opinion as a true fan:
The casting was good. The fashion was just like the cartoon. The pronunciation was correct. The sceneries were great. The bending looked great when it was actually used.
I rated it 3/5 because 20 episodes of the cartoon were shoved into 8 episodes and it was not perfect. The pirate arc, the northern air temple arc, not to mention Aang and Katara did exactly ZERO waterbending training together. Also this live action version did not capture the comedy from the cartoon at all. The cartoon was the perfect balance between the seriousness of war and the playfulness of the children. Also the actor for Aang needs to stop with the vocal fry, it is going to damage his voice in the long run.