Such a good introduction to a great series. Applegate manages to cram a lot of information and story into this first volume. It's even aged pretty well considering it was published ~20 years ago.
I did have a few questions on this reread, but I'm pretty sure they'll all be answered in future books (why doesn't Elfangor morph at the construction site)/they were pretty satisfactorily answered in this one (why didn't everyone acquire more morphs at The Gardens?).
The gang isn't as careful as I would be if I were secretly fighting an alien invasion but that never bothered me as a kid and it doesn't bother me too much now. There is the weird assertion that human can use thought speak that's never mentioned again if I recall correctly, but that's an easy mistake to ignore.