The Decision is a pretty fun book. We're seeing the storyline from The Warning pay off. It would have been nice if the book were a little longer with the second half of the plot filled out a little more, but as it is this is a pretty decent book.
I'm super excited because MM2 is next followed by what I remember to be some of the best books of the series (19-23 + The Hork-Bajir Chronicles).
Questions under the cut, spoilers as always.
If the TO had lived long enough could he have morphed and remorphed and regained his tail? I think this is explained in a future book, but I can't remember the explanation.
Visser Three morphing the Kafit bird (which had 12 wings, 6 pairs in The Andalite Chronicles, not the 6 wings it has in this book) 1. could be a message but 2. could also just be a morph Alloran acquired before he was a Controller. A Yeerk in the head doesn't affect DNA/morphing abilities. And one traitorous Andalite doesn't mean the Yeerks have infiltrated the Andalite home planet.
There are several times Animorphs are shown using thought speak while not in morph. There's also a use of the word "cripples" which, really? I think Ax has had nachos at the food court before.
ETA: I don't know that it ever occurred to me before, but why did they place the central arming unit in a place so difficult to access? Is it that thing of if it's hard they'll really think before they do it?