I read these books when I was in late elementary school through 7th grade. I am posting all of them which I own. When I was younger I really enjoyed them.
My daughter read it cover to cover in 20 minutes. Great book
Cassie's had it. After the last mission, she realizes she's getting tired of missions. Tired of battles. Tired of being an Animorph. She decides that she just can't do it anymore. So she quits.
But that's not the worst that happened. It seems a human-Controller named Karen followed Cassie after the last run-in with the Yeerks. And she knows Cassie is an Andalite...or human. Either way, if she exposes Cassie, it's allover. No more Cassie. No more Animorphs. No more planet Earth...
As an adult, I really enjoy reading this series. Some of the things usually aren't what kids would think about, in terms of ethical issues, but I would hope it at least encourages some of them to to ponder it. This book is a good, quick, read for any age.