Here's where the major spoilers come in - as copied from Wikipedia:
In the movie, Ellie (Allie in the film) rather than Will is King Arthur. Rather than Marco, Mr. Morton (Mr. Moore in the film) is Mordred, whereas Miles is Merlin as opposed to Mr. Morton. Marco is a member of the Order of the Bear determined to protect Will. The climax battle scene occurs in the ravine in the book, but occurs in the school theater (which magically becomes a beach) in the movie. Presumably, this is to make the film more unpredictable. Also the students are the reincarnations of the actual characters as oppose to merely corresponding to them. "Allie" is an only child, her brother is no longer a character. Will's father is not trying to make him join the navy. Will does not sail and does not have a dog, therefore there are no connections to the names of Arthur's dog and boat. (Will is not Arthur, hence the elimination.) Avalon High's team name is the Knights, not Excalibur. Many scenes were cut out and scene settings were changed to make the movie more appropriate for younger children because the book has violent and some threatening scenes.So basically, they switched around all of the main characters. I was quite disappointed by this, but I think it could have been pulled off if they had added more threads into the story. The most annoying thing was that since Will wasn't Arthur, all of the little things which made you think he was Arthur seemed pointless, and no extra interesting things were put in to point towards Allie being Arthur so it made everything seem very random instead of destined as was intended.
Thoughts on the characters:
- I liked the portrayal of Allie by Britt Robertson, I thought she held the movie really well. She's actually the reason I came across the movie as I had searched her on imbd after watching some episodes of 'Life Unexpected' (really enjoying it :D). She didn't really have the right look for the character if you're thinking about the book, but with the decision that she was to be King Arthur, I think that her appearance was quite appropriate.
- I loved the character of Miles, despite the fact he wasn't in the book, I really enjoyed the performance and he's quite a loveable character, perhaps the only character aside from Allie that the writers had decided to try and give any depth.
- What can I say about Will... I thought he was ok. The look was fine, I think, but the way the character was played really lacked depth. This was probably mainly down to the writers, and with the decision that he wasn't Arthur - they must have decided not to really focus on his character... To me, he came across as perhaps a little slow and naively happy - kind of reminiscent of James Marsden's portrayal of Prince Edward in 'Enchanted' (which I love btw). He's supposed to be some deep thinker, but I really wasn't seeing it.
- Lance and Jen barely got any screen-time apart from their secret looks and meetings which meant their characters didn't really get a chance to have any depth, and they were clearly there just to provide the love triangle (which didn't really have any significance since Will wasn't Arthur).
- I liked the casting for both Marco and Mr Moore - they would have still fitted the characters if the script stuck to the book. Marco had an unfortunate, very cheesy line towards the end - something like "I was only doing it to keep you safe. Treating you guys like that was the hardest thing I've ever had to do."
- I quite liked Allie's parents - they fitted the roles quite well, and fitted well enough with my ideas from the book.
Thoughts on other things:
- The 'flashbacks' were quite interesting, they were a useful way of showing the connections between people, and they fit well with the idea of Allie as Arthur.
- Really disappointed with the destruction of any meaning or depth in the circumstances in comparison to the story of Arthur. E.g. Lance and Jen losing their significance with 'Arthur', all the little things there were about Will in the book that pointed towards him being Arthur (names of boat, dog, etc.), the relationship of 'Arthur' to 'Mordred', well, you get the picture.
- There were some very cheesy lines in there - but hey, it was a Disney film.
- The special effects were interesting, very Disney-ish, e.g. the theatre transforming into a beach with fully armoured knights, the sword becoming Excalibur, Mr Moore becoming Mordred - Arthurian style.
- The removal of the whole 'Lady of the lake' thing was disappointing - I suppose they had a different surprise instead, but I don't think it was half as good...
Anywho, on the whole, I think that as a Disney film, it's quite a fun one to watch, a little cheesy, some entertaining special effects and a completely unrealistic appearance, all pretty good. However, in comparison to the book I thought it was quite a disappointment. As long as you don't start watching it with the impression that it's actually going to be the fantastic story you've read with interesting detail and back-story links, then I think it's still quite an enjoyable movie.