Toph I'm still slightly meh about, but Aang I thought, that was pretty interesting. I really think that's been blown out of proportion by the fandom, Kya and Bumi weren't estranged from Tenzin or anything. And Aang had good reasons to give Tenzin somewhat more attention then them sometimes.
The origin of bending isn't a retcon at all, and this one isn't really a matter of opinion. The lion turtles granted people the power of bending initially, and later they learned to use it from the badger moles, dragons,Sky bison and Tui/La.