The Lion, the Witch, and kids during wartime
The non-spoilery comments: overall, a joy to watch. They tweaked and fine tuned, cutting some things from the book, adding things that weren't there. All of it was in service to the story and greatly enhanced the character story arcs. I couldn't find any scene that struck a false note or was maudlin or sentimental, which was a big danger in adapting a story like this to a movie children could safely go see. The director has a sense of humor and a sense of drama and menace. Also, wow, a script. And character arcs.
As for the Great Debate (fantasy? or Christian Allegory?) it was really irrelevant. The Christian allegory is of course present but is kind of absorbed into the greater overall adventure story, and the emtional themes are universal. There was only one moment in the whole movie where theologically, I twitched, not in revulsion but just because it jarred with my own personal worldview. It's actually something that's a problem with a lot of sword and sorcery kind of fantasy, not necessary the Christian viewpoint.
When Aslan explains to Peter the nature of the deep magic, he says it defines good and evil and directs destinies (I'm paraphrasing). I don't recall if this is in the book or not, put just that way. Internally, that is, within this fictional universe, I have no problem with that. It's how the magic works in Narnia. But what happened to free will? Even within Christianity, there's the concept of free will so it's maybe not even so much a problem with the Christian allegory but with C.S. Lewis' philosphy. I'm going to leave it there because to follow that thread I'd need to have read his Christian writings, and have a better understanding of theology.
For fantasy in general, I'm not fond of prophecies and I like it when characters determine their own destinies rather than having them thrust upon them. This is, oddly, why the idea of the hero who grows into his role, or the reluctant hero, fascinates me. Prophecies or not, I think most fantasy heroes act out of choice, because they realize that if they don't do this, more people will suffer.
The film cranked up the "reluctant" part quite a lot, with the kids insisting they weren't heroes and at one point Susan, I think, tells Peter "Just because a man in a red coat hands you a sword that doesn't make you a hero." Which gave me an unfortunate Monty Python flasbback, but you know, the theme is the same. It's not the sword some watery tart or man in a red coat gives you that makes you King, it's your actions.
The film starts with Edmund breaking the rules and not listening to Peter, running back into the house to get the picture of their absent father. The addition of the London bombing scenes at the beginning was the largest change from the book and it worked so very well to lay the groundwork for the character arcs. Throughout the film, they keep coming back to Peter telling Edmund what to do and Edmund being the rebel and never obeying. Sure, Edmund's got problems, but I also thought Peter was overwhelmed, and therefore made a bad situation worse. Peter's struggling to be the protector and hold it all together but it keeps slipping from his control and his shoulders aren't quite broad enough yet to support it. And he knows it. So Peter snaps at Edmund a lot and makes mistakes that help drive Edmund farther away. I felt so sad for him.
Also having Edmund so determined to go back to the house for Dad's photograph was a nice character point that helped explain why Edmund is so confused and headed down the wrong path. The kid's just traumatized--it's easy to imagine how the father/son dynamic might have been for them and either way, his father's absence is tough on him. (My guess is that either Edmund's the favorite and they're close--the father being much tougher on Peter, the eldest--and Edmund worships him. Or that Peter's the father's favorite and Dad's much harder on Edmund and Edmund still worships him).
Interesting touch, that in a fantasy world where destinies are already determined by deep magic (supposedly), Edmund saves the day by disobeying yet again. (Also, the centaur gets turned to stone because he didn't listen to Peter shouting "Stop!") I'm not sure I ever quite got that dynamic from just the book and it's an interesting addition (like Boromir being tempted by the ring in the movies but not the books, it's an alteration that makes perfect sense).
Peter was book Peter in a lot of ways--he's always been bossy and overcompensates trying to protect his younger siblings and I've always picked up on that in the book, but it was nicely highlighted in the movie and turned into an actual thing. I'm not sure it's quite as much of a thing in the book. One of my favorite added moments was when Peter looks up in the train station at the beginning and sees a young soldier. The actor shows you clearly that Peter's having a "why him not me" moment. Survivor's guilt? Wanting to identify with the absent father? The character is old enough to identify himself with the boys going to the front and it seems like he wishes he could do more. But instead he's going to sit in the quiet countryside and babysit, safely hidden away. Or so he believes. Once he gets to Narnia, though, he's actually reluctant to take up the role of warrior, which is an old theme: boy longs to do glorious important things, but longing for it and then being faced with actual combat are very different. So Peter finds out what war really is, makes his first kill (that scene was so well done) and finally figures out how to be leader/protector.
One other thing about the war. From the original book, but highlighted in a big way in the movie, is the theme of children's helplessness during war. The Pevensies get empowered by going to Narnia. They can't do anything about the war at home but Narnia is a place where children can help restore good to the world. It's less terrifying for them to be involved in the struggle in Narnia and be scared there, than it was for them to be huddled shaking in a bomb shelter.