Why all the Cassie hate?

[Dylan]

Yay! That's my favorite in the series. I like the theory.
I also like The Sickness, The Unkown, and The Ultimate.

[Snakie]

Am I the only person here who loves The Departure?

Not at all! One of my favorites.

So many things were happening to Cassie all at once and it was all catching up to her, I don't entirely blame her for quitting. Nor do I think it's too far off for her to trust her gut and take a huge but calculated risk when she believes her life just hit rock bottom. I think her actions would have been infuriating to me had she not been cautious and subtly learned more about Aftran before revealing herself. I think, and this is just my personal theory , that once she did, she knew how to convince Aftran, what actions and points she had to make. I think Cassie learning about how shaky Aftran and other yeerks' likely conditioned-from-birth thoughts about sapient life were, namely Yeerk vs Human life, may be what made it possible for Cassie to figure out how to change that.

I wouldn't doubt that Cassie specifically didn't demorph even when Aftran begged for her to, partly because she did want to keep her word to the letter, but also because she knew that it would hit the nail on the coffin, that it'd strongly impact Aftran (who seems already easily affected by the emotions of their child host, is also feeling their own sense of responsibility, guilt, trust, and appreciation for the sacrifice she made) enough to shake everything they knew.

That's just how I saw it, anyway. I think I need to get on with my reread to jog my memory though.

I love #19 despite the fact that its Cassie at her most foolhardy and quixotic.

The only weakness in the story in my mind is the cop-out metamorphosis=morphing ending.

[Chad32]

Well, they had to get her back somehow. It is a pretty big stretch, though. I don't even know how long it takes for a caterpillar to turn into a butterfly, but is it less than two hours?

[NickDaGriff]

Weeks, if I remember my first grade teacher's butterfly project right.  And even then, going nothlit means your original body is lost in Z-space.  Even if it somehow suddenly reset the morph clock upon emerging from the chrysalis (which makes no sense, it's just normal insect puberty, not altering DNA or anything, no real catalyst there), butterfly should've become her new base morph, the same way Tobias stayed locked into hawk to regain his morphing powers.

Makes no sense at all.  I call Ellimist shenanigans.

[Chad32]

Deus ex machina, aka Ellemist shenanigans. Not like Animorphs is the only series to have a DEM, but it's lucky enough to actually have a character in universe that can reasonably do it.