Here's what's appealing about it for me. Zuko has never really been evil. He just thought that the Fire Nation was the good guys and that they were helping the world via the war. Betraying Iroh at CoD was the first time I think he ever saw himself as having done something authentically evil. He has a lot of character and even spoke up against a military general in his father's war room in an attempt to save FN soldiers. Because of that, Ozi did...well, Ozi did what he did. He lost his mother, which left his father, who favored Azula more, as his only parent. He really has had to struggle to make it to where he is and his character shows that. Even his enemies have acknowledged that he never gives up.
Aang ran away from his responsibilities because he didn't want to be the avatar. Once he woke up from the iceberg, he's basically tried turning everything into a game as much as possible. Now, there's nothing wrong with fun every now and then, but it's too much when the world's fate is at stake. Even now, he isn't responsible. Zuko had to convince him to go all the way through with the task during TFM.
Katara has lost her mother, had her father leave to go to war, had to teach herself waterbending for a very long time, and knows when to take things seriously and when to have fun. Even when Zuko hung her mom's necklace in front of her, she picked the safety of her friends over the necklace. At the North Pole, she stood up against Pako (sp?) and the entire culture for her right to learn waterbending as a martial art. She's a person who is willing to give second chances to people, values the safety of people who need her over her own guaranteed well-being, and has come very, very far as a waterbender.
(God, listen to me. I'm talking as if these characters really exist. :p )
Basically, Zuko's got character and he deserves the girl that's got it too. A lot of times, when the spotlight is on them for the episode, they're fighting uphill battles. Aang's challenges, to learn all the differnt bending arts, seems to come so easy to him and his character shows that. It hardly takes him more than an episode to get good at it.
I'm not saying that Aang should be punished for being gifted, I'm saying that Zuko and Katara should be rewarded for having the personalities that they have.
