I liked the teashop reunion scene, but also agree that some indication as to what happened to Zuko's mother would have been satisfying as well. I certainly don't blame the writers for not having done that, given the funding situation. If we ever do get the answer, however, it may not be what we think, because we're all assuming Ozai actually told Zuko the truth about what happened that night.

It must be said that one of Ozai's best bending abilities, which he still has, and which he shares with Azula, is bending the truth to suit his purposes, and he was trying to emotionally jerk Zuko around at the time he supposedly revealed Ursa's fate. It's quite possible that what actually happened was that Ozai's punishment was to be passed over in the succession altogether in favor of Zuko, with no chance of ever becoming firelord even if Iroh didn't want it. If that were the case, Ozai might have assassinated Azulon himself, then lied to Ursa (and Azula, and the people of the Fire Nation) about what Azulon had said. He might have let Ursa think he had killed his father to protect Zuko. Ursa may have agreed to take the fall out of gratitude for his having "saved" their son, thinking that Zuko might still be in danger if there was any suspicion that Ozai had murdered the firelord. Or Ozai could have blackmailed her into it with Zuko's safety as the price. It's not really clear what their relationship was at the time. It also never made sense that a man who loved his son as much as Azulon obviously loved Iroh would just capriciously do away with his innocent (and at that point only) grandson. Disinheriting Ozai would have been a more just solution, as Ozai was the one who had angered him.

Whether that's the truth or not, I would have liked to have seen more, in flashback, of Zuko's family when they were happy, and why that changed. Did that begin when his mother left? And there are so many questions unanswered. How much did Ozai love Ursa? Was part of his overblown anger at Zuko's "disrespect" and "weakness" fueled by having lost her for Zuko's sake? It was hard to tell, in the episode which showed these events, whether Ozai's reaction to Zuko's questions about his mother's whereabouts immediately after Azulon's death was caused by grief or coldness. I guess that's really an indication of what a good story this was, that there's so much you can wonder about, and read into it.