Kinda feel like Battle Angel Alita needs to be mentioned.
The original series was a masterpiece if you ignore the ending by the replacement author.
Last Order picked up where the original author had to leave and started interesting and presented a fresh, big universe for exploration, but then it devolved into an overlenght tournament arc with an overlength flashback arc to stretch the whole thing even further. By the middle point of the series, Alita was a sidecharacter in a series named after her.
And now Mars Chronicles is continuing the trend of flashbacks within flashbacks.