OSC is good for starting a series with a punch in the jaw and then letting it trail off. The Andrew Wiggin stories are NOT an example of this, however. If you want to see more of that, look at the Homecoming series, or the Tales of Alvin Maker as prime, painful examples.
Bear in mind that I have only read the direct sequels, not any of the parallels.
Ender's Game was the punch in the jaw. It was ugly, brutal, inhuman, dark and painful. It was about the deliberate deconstruction and reconstruction of a person, destroying his childhood and replacing it with a cold, calculating killer. It succeeded in absolutely every respect and the fans, as always, wanted more. Card decided to oblige. Luckily, Card is a smart man. He knew that there was absolutely no way to follow up Ender's Game. Its a complete-in-itself masterwork. Trying to create more of the same would have resulted in a poor imitation that only served to tarnish the first story.
He instead chose to shift the focus, make the story more thoughtful and more moral and ended up with Speaker for the Dead, Xenocide and Children of the Mind. Card decided to follow the rest of the life of Andrew and his sibs. The summation at the beginning of Speaker for the Dead, to catch us up to the far end of Andrew's life was wonderful and served to distance us from that brutal story, while setting the stage for an examination and partial resolution of his guilt for the terrible thing he was created to do.
