Hey, it's Shen. I'm gonna give my two cents, given that I'm exploring the site out of boredom.
I agree with what everyone says about the ghostwritten books being bad. In fact, they were actually so bad that my twelve-year old self could never finish the series. K.A's writing was engaging and beautiful, and when I re-read the earliest books as an adult I find myself just as entranced as I had been then. Because I heard through word-of-mouth how badly the ending came out, I just abjectly refuse to finish on "moral grounds." XDD I want to preserve my memory of what I loved about the series, and simply will know how The End came through the usual sources. ; )
I personally still think Animorphs is good. Re-reading it, I was shocked to find that it was perhaps even better than I'd expected. KA always threw in political nuances and themes on the nature of freedom, the pain of war, and the gray shades between good and evil. Few book series that are written for pre-teens/children have ever done anything like this, and I'm frustrated that the political climate has created a saccharine sweet politically correct media climate. You can't blame the kids today for being so distanced from reality. Animorphs, while grounded thoroughly in science fiction, wasn't afraid to describe the way that the world could be harsh.
In particular upon re-reading some of the books, I almost laughed at how uncensored it all was. I was eight years old when I began this series, and I was reading about pain and suffering and screaming and death? XD It made me wonder just what kind of kid I was. ; ) The series is also part of what has formed my worldview, which includes the belief that people are rarely what they are for no reason at all.
I still think the characters are fairly impressive for a book series like that, despite KA Appelgate's memory lapses. X3