The "David Trilogy" is pretty much what made me want to come here and discuss them, I just recently read them for the first time. I really love/hate them, its a hard read emotionally.
I will say that the parts about the Summit and the World Leaders is lacking, and feels like it only exists to give David a mission to go on, nothing really came of it.
The books have changed how I view the Animorphs, and especially Cassie. This is the first time they have made some big mistakes and done something morally repugnant out of necessity, I am not much further in the series (only at 24 as of this post) but I know from other discussions I have seen that it goes in a darker path after these books.
David as a character is not the best, I think we are supposed to see him as crazy if not evil, and he changes from being a scared kid to that way too quickly. I know he is hated by a lot of readers and see it as he got what he deserved. I can't help but pity him though, I think if the Animorphs had handled him better and not been so cold to him it would not have turned out the same way, Marco especially pushed him away from the group. Maybe I feel so bad for him because I identify with David a lot, when I was around 14 I was a problem child (granted I never tried to murder anyone) but I know what its like to be a loner and have emotional issues, and violent tendencies. I was lucky enough to get into a new home environment and turn my life around. And I cant help but think David was not beyond saving either, and there were other solutions besides the brutal one the Animorphs used. (If David is supposed to be a sociopath, someone who genuinely cannot improve as a person, I do not think Applegate displayed it very well, and all teenagers at that think like psychos, theres a reason it cant be diagnosed until 18)
I think the Animorphs choice to turn him into a Rat, was overly cruel and a selfish act. They are kids and they want to be the good guys, they dont want to have the blood of someone else on their hands. But I genuinely think it would have been better to just kill David instead of condemning him to live as flea ridden rat alone on an island going insane from loneliness. Its something I wouldnt wish on my worst enemy, let alone a child. (I know he comes back at some point from spoilers but I have not read that yet) Yes he tried to kill them, and possibly killed Saddler, again I would even be fine if they just ended up having to kill him in a fight, but the rat plan was way too far. My views on Cassie changed a lot from this, she is the soft hearted one who wont kill and came up with this plan. I see her less as someone who was empathic to manipulative, and she was already my least favorite Animorph.
I guess they did what they thought was right, but I think this is the first time I cant look at them as heroes anymore.