I haven't read any of the other books, and I actually thought that Ender's Game was a stand-alone book until I looked at the list of books under this series that was nestled among Card's other works just before the title page.
Even if Ender's Game did not have a continuation of books after it, it would have been equally as good. Because it finishes with a few loose ends and questions unanswered, it leaves room for the reader to imagine what happens to the characters and even the entire human race. Instead of going out with a bang it slips into a quiet thank you, and it almost feels like for the time being everything is alright.
So as you said it is reasonable for the type of storytelling to change as Ender gets older, but even without us continuing with him on his journey the first book suffices.
Even if Ender's Game did not have a continuation of books after it, it would have been equally as good. Because it finishes with a few loose ends and questions unanswered, it leaves room for the reader to imagine what happens to the characters and even the entire human race. Instead of going out with a bang it slips into a quiet thank you, and it almost feels like for the time being everything is alright.
So as you said it is reasonable for the type of storytelling to change as Ender gets older, but even without us continuing with him on his journey the first book suffices.