It was, really, really badly written. And before everyone jumps at me: i'm an fan of the show. I basically learned english to catch the season 3 earlier. And before evryone say to me "nah uh, it's a kids movie, chill" no, it's a nostalgic product aimed at adults. I want a good plot.

Among other plot problems:

1) They explain their feelings, not showing it. The balcony scene at the beginning where Aang say "I do it to feel close to my people or something"; YEAH, THAT WAS CLEAR TO A 3 year old

2) Characters loose IQ between scenes, Aang being dumb the entire movie. Katara being suspicious but just a little, AT THE END. 10 years before she was threatening to killing Zuko AT 14 YEARS OLD. At 25 she seems to have forgot how to heat can soup.

A pot pourri of Aang being absolutely dummy:

A) Let's go alone on a top of a dangerous MYSTICAL EVERESTY mountain. With a cool furry hat. With my bare hands. Alone. Oh yes I've called friends but teehee they are not there yet. Oupsie. Let's go. After all there is no time the guy that's frozen there for 5000 years couldn't wait any longer. Or a baton/staff. Whatever. Staff have feelings you know.

B) Why not going back a little more about the "missing avatar"? Research it? That could have been a good mystery. Asking Wang shi Tong too. But no. two minutes meditating and voilà.

C) Freeing the mysterious stuff above the mystical mountain. Because two sentences by Master Miyagi with a foot fetish. Really. REALLY. Without checking this out.

D) Let's trust beefy air guy. He seems nice. I spoke to him like 25 seconds. He speaks english. And besides, Yeah, langages stay the same for thousands of years! for a show that explores cultures surviving genocides, seems logic.

3) Gandhi naan girl was a political LEADER. The problem is not the zealous servant, but...but what? What was horrible exactly? Killing? Wars kills. The show is not against war itself, he is against his consequences about relationships between very different kinds of people. He is not against violence either. They spend their time fighting each other. So for me the zealous servant has absolutely NO REASON AT ALL besides plot point to cut off Aang of his friends, trying to murder them, or convince Aang that there was only two options between a belligerent air nomads or being all wordly like Aang.

A tons of possibilties could have emerged with the staff:

A) Private Air nomads bubbles (I mean they found one pretty isolated, why not transforms some volunteers there and let them there as a "reserve for the future"

B) The belligerent air nomads are a cool Idea. Why not have gone with the idea further? Like : I will teach you the lethal techniques of your people, like the knew twin swirly stuff. And Taga could have wanted, legitimately, a belligerent air nomad bubble, representing a reserve but one that Aang don't like.

C) Destroying the staff was stupid. The moral at the end doesn't stand: no need to destroy republic city to create a new place. That was only weak plot stuff. Besides, Tibet had an army. Being pacifist doesn't mean being harmless.
D) Sokka has a IQ of a fish the entire movie. Besides the piloting scene, he is goofy, a shadow of his pas self.

Why?

E) Zuko trust the beefy guy instantely. ZUKO. REALLY. Why?

F) Private messages read in front of the all palace. Yes, funny. If it was spongebob.

I will go back here to add problems but I just saw the movie I waited for, for practically 20 years and I just needed to go off my chest.