look on the bright side, it leaves room for fanfic.
and what's with wrong with ending in a cliffhanger?
Have you seen most fanfic?
Most fanfiction is terrible. It is either badly-written with obvious Mary Sues/canon Sues or serves as an outlet for the sexual fantasies of the author. Often it's both.
With the exception of Augustine Quill's fic, I don't think I've ever seen a well-written attempt at explaining the ending of Animorphs. (I haven't read any of the fics on this forum, however.)
I think a cliffhanger is the worst way to end a series. I like endings that give you conclusion, not ones that make you wonder even more. The story doesn't have to end with everyone living happily ever after with their lives spelled out for them, but drastically changing the story in the last book and having an ending that made no sense within the context of the story is awful.
The ending was badly-implemented. Instead of finding a way for Rachel to solve her problem with violence she's just killed off - what's the point of exploring both sides of Rachel if the author is going to treat her one-dimensionally anyway? It sent the message across that people with any degree of mental illness can't recover.
I hate when people say that the Animorphs ending was "realistic". It's a science fiction kid series, and besides, you can write a "realistic" ending without cheating all of your characters out of a good futures. It was a miserable failure in terms of evoking sympathy for the characters - if I want to watch something sad I'll watch The English Patient. The ending just angered me because it was badly-written and rushed.
Was anyone else angered by the "message from the author" at the end when she asked us to check out Remnants? I felt like she was sick of writing Animorphs so she rushed through the ending and went off to write another series. Regardless of whether or not that was her intent, it certainly came off that way.