I read the entire series several years ago. I was glad that the movie was true to the book. The only license they took was the waterfall/iceburg scene.

I wish the father christmas scene was done better to show that he was actually acting as a prophet.

The war scene at the beginning was also an incredibly delightful addition to the story line.
The book assumed everyone know about the bombing raids so Lewis only referred to them.
Since 6 decades have passed it was necessary to elaborate on them.