This is one of the novels of the Narnia series that I loved the most. Mind you, that doesn't make it the best novel of the series. It's episodic nature is a serious problem. But, it is forgiven in light of some exciting scenes and wonderful imaginary places.
The movie is mostly true to the book, and if anything improves on it a bit. It starts with the two youngest children, Susan and Edmund are staying with relatives and have to deal with an obnoxious brat named Eustace Scrubb. Luckily, they are all sucked into a painting and taken back to Narnia. There they find themselves on the good ship Dawn Treader as the King seeks some missing Lords. So they travel from one mystical island to the next learning lessons and having adventures.
The movie, as I said actually handles this better than the book by tying it all together better with an overarching mystery involving some evil mist. Unfortunately this only takes us about 80% through the movie. The film sort of speeds through the ending which is sad. There is some real wonder on the way to Aslan's country that is just a tad glossed over for my taste. Still this is a very well done adaption and I enjoyed watching.