man. I remember just sort of... sitting after this book. The Revelation changed the status quo of the series in a way nothing had before since...
well, honestly, since Tobias got his morphing back.*
Like, there were things in between (The David trilogy, Visser, etc) that changed the status quo of the overarching plot. The Animorphs gained control of the Escafil device. Visser One's fall was pretty huge in terms of the actual war. Major changes on Leera and the Hork-Bajir homeworld start putting pressure on the Yeerks across planets. We saw slow but steady development of the characters that set up their choices as we enter the endgame as well.
But this was the biggest shake up in the formula.
Marco's no longer schoolkid by day guerrilla by night. There's no returning home or using a secret identity for him anymore. His family is reunited at a high cost.
Yeah, Visser Three's impending promotion is a dread on the horizon, but what stuck out as a kid was that I no longer had quite the same "safe" feeling that I could expect things to turn out well. In some ways I think the "filler" books added to the impact of the game-changing one because I was so used to the "everything resets at the end of the episode" feeling I'd read as a kid who focused more on the six main characters than the progress of the overarching war.
It hit at the right time for me, I guess. I was just starting to get old enough that the not-quite-resets had begun to bore me but I hadn't hit a wall with it yet when this shook everything.
And man, did it scare me to realize the next book was breaking the narrator pattern by going from Marco to Ax instead of to Jake.
*The David Trilogy is in a bit of an odd spot here. When reading them in release order yeah, they were game changing. A new Animorph? Who just killed Tobias? But Tobias is revealed to be alive and David gets turned into a perma-rat and the set was labeled from the start as a trilogy so taken as a whole I didn't register it as game changing since they didn't use the morphing cube again for a very long time.