A lot of you are upset last night's finale. Did not like the sad ending? I went to sleep, and thought about it, and it makes perfect sense.
They have 20 more episodes next season to fill. Sometimes you need bad things to happen, to create conflict and fill up 20 episodes.
We got Zuko making the wrong choice, no doubt about it, but having regrets. If it made the right choice, he would have no regret, no conflict, what is there left to do?
Aang is injuried, he has recovered. That has another few episodes. The writers got to do, what they got to do.