The Stand to Reason blog says the film is enjoyable, but unfortunately it downplays the main character of the series:
Here’s my main criticism: The filmmakers still don’t get Aslan. They’ve made him a character rather than the character. Because of certain changes here and there, he lost the authority he should have radiated and didn’t inspire the awe that Aslan should inspire. I think there are a few reasons these things didn’t come across (minor spoilers ahead). First, Aslan is not central. In the book, a few of the main characters do not believe in Aslan (until he shows up, of course), and this fact is often pointed out and discussed. The question of Aslan can’t be avoided, and everything leads to Him. When these moments are removed from the story (as most of them were in the film), Aslan isn’t just away from Narnia, he’s inconsequential to it.
“He is the image of the invisible God, the firstborn of all creation. For by him all things were created, in heaven and on earth, visible and invisible, whether thrones or dominions or rulers or authorities — all things were created through him and for him. And he is before all things, and in him all things hold together” (Colossians 1).
Update: John Mark Reynolds thinks the movie is actually better than the book.