|Image from Buena Vista Pictures|
The Narnia series is not a complicated or lengthy story. There aren't that many words involved and each one was carefully chosen by Lewis for a purpose. There are simply some works of literature that don't translate well into movies...particularly when those movies are produced by a secular source that has revenue as it's primary goal.
Incidentally (not that you asked), I think they messed up Lord of the Rings as well. The cinematography was marvelous but the substance was a flop. My husband and I stayed up late one night to watch it, decided it wasn't worth losing sleep over and shut it off. I know the story so well that I was bored without the abundant and important details of the book and annoyed by the inevitable liberties taken by the movie writers. They got the bones of it right but left out the heart.
Perhaps I'm coming across as a bit of a book snob, but unless a great work of literature begins as a screenplay, I suggest that it's probably better off left in print.