In my own feeble attempts to write stories I have found two methods for crafting a good ending to a story first you have an end you want, then you shape the rest of the story too lead to that end. Second you write the story you want then shape an end that concludes it. The important thing to both methods is using everything you have done too those characters in the final battle. Every joy and pain, love and lost, friend and enemy must find a place in how they react, win, lose, and die.
I do not think KAA did either, she had an ending in mind at only as far back as MM4: Back to Before in order to make that end fit she hammered the Animorphs into it and ‘forgot’ things that would have made her ideal ending difficult. This is the reason so many people did not like the final. Both of them.
I personally would have made a far bloodier and painful end where thousands died in outright war,the yeerk empire fractured in several pieces, and 2-3 animorphs met their death.
The happy end I can only see if everything after book 10 was redone and the series ended after 30 books
