In the book, Susan fires a warning shot. In the movie, she shoots the soldier on sight, when for all she knew he was legally executing a guilty prisoner (what made them think the dwarf was innocent, after all?) These are the types of situations that are often glossed over in movies, and I really wish people would rethink them - the good guys are only good if they are, well, good! They can make mistakes and be human, but if they commit a seriously evil act, someone should at least consider it a mistake - it isn't okay just because they're on the good side!
That's one of the things I love about Tolkien - he makes his plot work, but never sacrifices his characters to it. Aragorn does not take the expedient action, but goes on a wild goose chase to try to save Merry and Pippin. Forget the Ring, forget his throne, forget the war...he has to save two little hobbits. He has no help to send, so he goes himself.
Of course, it's a story - Tolkien can orchestrate fate and chance to make these types of decisions pay off, coincidentally or otherwise. But movies are stories, too, and I wish they'd think through consequences to character a bit more.
It took me awhile to get the hang of what was going on in the duel, but again, Hollywood does not understand ethics. If you are participating in a duel to the death, you are not a bad guy if you kill your opponent when he loses. But how many movies have we seen where the good guy shows mercy and just can't bring himself to kill the villain...only to have the villain killed immediately afterwards in some act of chance or treachery? (okay, so Tolkien does that too - with both Saruman and Gollum - but he has plenty of fate and mercy and prophecy to make it make sense!) Poetic justice is a beautiful thing, but instant karma can get a bit old.
I'm not upset with Peter or Caspian for hesitating. Both of them have good reasons to pause. His opponent has called respite, so Peter should (from the point of view of chivalry), grant it to him (even if Edmund the Just disagrees). And Caspian can't very well just execute his uncle in cold blood (he's not part of the duel). What bothers me is the suggestion that Miraz has a point - that if Caspian kills him, he's 'just like Miraz' because he killed a relative to get the throne. Caspian is the rightful heir to the throne, while Miraz is an usurper. This distinction matters, and they've practically wiped it away to say 'kinslaying is kinslaying.' If you accept this premise...then the Old Narnians don't have a leg to stand on in the subsequent battle. Instead of them fighting to get the true king on the throne, they're just fighting to get their king on the throne.
I realize it's not that simple. The Narnians are under attack - their choices are basically to fight or die. They're not given much of an option. They're defending their position, and they're underdogs. So, sympathy is generated appropriately. But to make them be right...well, the movie doesn't really bother with that. And that bothers me a bit. You can be cynical and argue that there is seldom a right side in a real war, and I will agree, but then you have to (as Frelga said), make at least some comments on the horrors of war.
As for the loss of the 'faith walk' Pearl - I think it was a timing issue more than anything. Aslan can't show up til the end. Peter and Caspian have to meet much earlier to have any time for character development in the movie. And so...they substituted the castle attack, where Lucy's decision to 'wait for Aslan' is contrasted with their decision to do something themselves. Lucy's conversation with Peter after the White Witch fiasco makes it clear that he's starting to understand what he's been doing wrong, and he comes around to her way of thinking. So, they still have that idea - just not that plot point. The 'Aslan icon' serves as a substitute, I suppose. I imagine that was the one single part left out that is most missed. I have not heard anyone complain that we didn't get to see Lucy and Susan liberate the captive school children and then dance with Bacchus' wild girls
.And Ben Barnes is a bit young for my tastes, but whatever makes you ladies happy
Just kidding, I agree that he is good looking and has a fun accent.
That could be a great movie, if done right. "The Magician's Nephew" has some very filmable scenes. And even "The Last Battle" could translate well, I think. 
