It's been a while since I've read the book, but as far as I could remember the movie stayed pretty close to the book. It did add in one little facet that isn't in the book, but movies like romance.
The book of course goes into more detail as to the spiritual reasons why some people could see Aslan and others couldn't. But it's always harder to get those things across on film.
One part I love in the story is when Aslan asked "But why didn't you follow me anyway?" Good question.
But later in the story she has the opportunity to demonstrate her faith as she stands alone against a massive onslaught. Alone, but for the mighty Lion at her side. I loved that image and I hope to keep it in my mind. I want that kind of faith. The armies coming against her appeared insurmountable, but she stood firm, her little dagger in hand. She stood because she knew the one beside her. She knew who he was and that all the power belonged to him. She also knew who's fight it really was. I want to remember that.
So, I recommend the movie. It was very well done and very exciting!