I really think there should have been an Iroh vs Ozai fight. The fact that they never so much as interacted seems like a missed opportunity. When Aang goes missing (being taught energy bending by the lion turtle) Iroh should have stepped up and decided that he had to fight Ozai. Taking a concept from the Zuko/Azula fight, Ozai and Iroh should have had an epic fight at the end of the series that seemed to be a stalemate. Zuko arrives after he and Katara dealt with Azula and Ozai should have shot lightning at Zuko which causes Iroh to jump in front of it and absorb it which would kill him. At which point Aang would appear and fight Ozai.
I didn't like how neat and tidy the ending was where literally none of the good guys died.
This ending is in the same bittersweet vein as the ending of the Hunger Games trilogy. How about I one up that? Why not have Aang and Iroh both die? Azula is dead, and Ozai was executed by Zuko himself during the fight after Aang gives the second to last final blow.
Katara discovers a week after that somehow she had gotten pregnant off camera, while Zuko becomes a Fire Lord that is left to pick up the pieces of his shattered psyche as the man who he loved died, and the friend that he trained to fight his father died as well. Mai can no longer take Zuko, which leaves her and Zuko together. They don't really like it at first, but she gives birth.No one dares question Zuko, but Katara's calming hand keeps him from boiling over.
The child is an airbender, and he's raised as Zuko's son. The second is a pair of twins, one a firebender and the other a waterbender, or one of them is nonbender. The airbender is named Tenzin in tradition of his father's lineage, while the others are named Iroh and Kya. Tenzin then establishes the Air Nation, with his father's blessing and freely gives the throne to his younger sister Kya, who has her parents' fiery passion and wit.
The United Republic is established in a different more brutal manner in between both shows, and is already its own republic with the help of the Fire Nation, with Tenzin as it's leading soldier who is a sort of figurehead as he fights against Kuei's insurgency and establishes the rights of the colonists as their own nation. In memory of his father, Tenzin has two statues erected of Zuko and of Aang which overlook each other at opposite ends of the bay. He then retires to Air Temple Island. Aang's legacy is one of him saving the world at the sacrifice of himself, while in some place far in the Southern Water Tribe, a little girl is born with the Avatar spirit.
I know the pregnancy thing looks unacceptable, but then again, I'd probably do a time skip a few years later so it's not all creepy as heck and that's why things are more drastic. Or that Roku's prediction was off by a year or two because he's been shown to be wrong, like in the comics where he called Aang to murder his great-grandson that helped fight Ozai in the war. But disregarding those, I still think he could just be wrong by a small chance.
Maybe if the show had taken place over the span of years rather than a little under a year would have made things a bit better.
I too wish we got to see Iroh vs Ozai let alone those two actually interacting.
A fanfic reinterpretation of the franchise, called Children of War, happens over three years instead of three seasons. There are many changes in the story, notably that each culture has it's own language, while a common colloquial tongue called Tianxia [The Earth Kingdoms' tongue, since Ba Sing Se is just a formality than a reality in this universe] dominates. Also has more distinctions in cultures, notably in the Fire Nation which has three different ethnicities alone.
And Iroh vs. Ozai fight even if Iroh or Aang both lost their lives, would be more meaningful than what we got. I sort of like the idea that's off my head that Sokka ends up delivering the killing blow to Ozai or Zuko, but because he's the everyman, it's unexpected. Having the idea the prophecies don't have to be fulfilled at all, would be the best way to subvert the chosen child tropes that Avatar up to the third season had done, and would be a nifty conclusion to the series in my opinion. Even if Ursa did come back, it would just be a bittersweet ending. Actually, I've always held a headcanon that Zuko and or Azula are actually Iroh's illegitimate children between him and Ursa and that he's the King Arthur while his father is akin to Merlin. He pulls the stone when he meets the Sun Warriors, and hasn't got back since. The reason why Ozai mistreats Zuko is because he knows he's a bastard ,but not Azula, who's far more competent than he is, [According to his own self perception of power versus Iroh's.]
Like how Buffy was supposed to die in season one's Prophecy Girl and have Kendra take over as the Slayer. She still dies, but Xander still saves her, creating an unexpected scenario of two Slayers, which would lead to the upheaval of the Watcher system due to them realizing that the Watchers need the Slayers more than the Slayers need them.