I recently saw the film version of C.S. Lewis' Prince Caspian. Like the film version of The Lion, the Witch, and the Wardrobe, it does a good job of conveying the book on the big screen. In some respects, the movies are actually better than the books (which is something I rarely think about movies based on books that are any good).
Especially in comparison to his friend J.R.R. Tolkien, Lewis wasn't much interested in developing imaginary worlds with believable cultures, political institutions, and visual texture. His main focus was on character development and religious allegory (the plot of the Narnia books is a deliberate allegory on Christian theology). As a result, Lewis' Narnia seems very underdeveloped compared to Tolkien's Middle Earth or the imaginary worlds in most other topnotch fantasy literature. Through their impressive visual imagery, the movies make Narnia "come alive" in a way that the books don't. I didn't need to see Peter Jackson's excellent Lord of the Rings movies in order to have a detailed image of Middle Earth in my mind. Not so with Narnia, which seemed basically flat until I saw the movies.
Overall, Prince Caspian is not quite as good as the first movie in the series. Most of the problems arise because the book it's based on simply isn't as good as The Lion, The Witch, and the Wardrobe. There's very little character development in Prince Caspian. The four Pevensie children from the "real" world are basically the same as they were in the first book. And the title character's development into a leader seems too swift and easy to be either compelling or believable. It's also hard to buy into the plot about the oppression of Narnia's talking animals by the Telmarines, because it just doesn't seem that severe. Here, the problem may be that Lewis had to tone the violence and repression down in order to make the book fit the standards of what was considered suitable for children in the 1950s.
Finally, the Telmarine rulers don't compare to the White Witch in the first book as a serious enemy for the protagonists. They seem too incompetent and stupid to be a real threat. To avoid spoilers, I won't go into details. Let's just say that the Telmarine leaders are even more badly in need of The Evil Overlord List than most other fictional villains.
The movie doesn't help matters by giving the Telmarines Spanish accents and dressing them up to look like Spanish conquistadors. I assume that the point was to analogize their conquest and oppression of Narnia's natives to the atrocities committed by Spanish colonizers in Latin America. But to me, the conquistador outfits made the Telmarines seem more silly than scary. In fairness, however, the Telmarines are relatively more dangerous and effective in the movie than in the book.
After seeing the movie, I wondered how it was that the pathetic Telmarines managed to conquer Narnia in the first place. One possibility is that later generations of Telmarines were less effective than their conqueror forefathers. Checking the book, however, I got a different answer: near the end, Aslan explains that there was internal "disorder" in Narnia when the Telmarines invaded. So perhaps they defeated the talking animals by taking advantage of a preexisting civil war or other internal conflict. Still, it would have had to have been a real doozy of a "disorder" for the contending sides not to unite against invaders who - according to both the book and the movie - were hellbent on not merely conquering the Narnians but actually exterminating them.