I agree with Cerulean above: '...they just need to have the time needed to tell the entire story'.
As exciting as a movie sounds, the way movies are being done now days, they tend to c-o-m-p-l-e-t-e-l-y miss the mark by focusing on specialFX, romance and self-contained happy endings. Trilogies and revamps don't fare much better on the big screen.
The Transformers movie is an example that fits the topic in question. They did awesome graphics and bumped up the impact of scary side of things, (I recall walking down the street and looking at parked cars in a whole different way). In that aspect, the movie was good. But the plot and the actors really made it a boy's crush-thing movie, and therefore totally lame for my digestion.
Nevertheless, I can't remember where, but I believe they are already making a sequel to the movie...
I would not be keen on seeing the spiffy way Hollywood would do Jake morphing a tiger, I can already imagine that. And I would certainly not settle for them doing a Jake+Cassie kiss at the end of something that should be waaaaaaaaaaay down the track. It would be a -ive for me.
And I can just see it, they would try to fit David in the movie package, too. NGHAAAAAAAAAARGH!
To me, the story of the Animorphs cannot be done justice in a 2 hr movie.
I would be more keen on a re-doing of the series. Done properly by some ani-fanatic and with a proper budget.