(1) The key issue, in my book, for any movie adaptation of VDT is how they handle Eustace. There are some strengths and weaknesses with this portrayal; they played him a little bit too much over the top for comic effect, but captured the pompousness about as it should be captured. The whole point of Eustace is that he is the Modern Boy, the boy who almost deserves being called Eustace Scrubb: failing to bring this out properly weakened the portrayal somewhat. And need it really be said that Eustace is not the sort of person who would do anything so old-fashioned as calling his mother 'Mother' rather than calling her by her name, 'Alberta'?
(2) Because of the episodic nature of the book's plot, tying this together into a cinematic unity is tricky, so there were bound to be hard decisions. Hollywood just can't do Immram very well, through no fault of its own: the limitations of the cinematic art sharply cramp any such style of narrative.. They did one thing very, very right: conflation of islands is almost absolutely necessary to making the movie move along quickly enough, and they chose the right islands to conflate. It's almost brilliant to recognize that Deathwater and the Dragon Isle could be conjoined for cinematic purposes. Reordering the islands was a serious mistake, and weakened rather than strengthened the story; and Lewis's original solution for breaking the spell at Ramandu's island was far superior to the Spectacle with which it was replaced. Giving Rhince a bit of backstory was much better, and the addition of his daughter was promising, but their fit into the overall arc was not especially great.
(3) It's perhaps not surprising that, despite some cutting of his part, Reepicheep is far and away the most engaging of all the characters in the movie. But Georgie Henley's performance as Lucy was, as all her performances have been so far, extraordinarily good within the limits of the script. She's the only movie-version character who has consistently been better on screen than the version I had already imagined, and most of that is due to the fact that Henley has the character down.
(4) One of the trickiest things about filming the Chronicles as a series is keeping the characters who have fallen out of the main story alive for when they come back (in one form or another). This is very excellently done here, much better than I expected.
(5) Really, the only thing that seriously disorders the movie as it stands -- it is far superior to most Hollywood adaptations in everything else -- is the Evil Fog thing. Pretty much every problem with the movie is connected to this diabolus ex machina. Perhaps, though, they can tie it in with the Witch of the Green Kirtle (and conceivably that was what they were thinking of, since that's the only halfway reasonable thing I can imagine them thinking of). The only other issue of importance is rightly noted by Wright:
As a purist, what I missed most was the medieval flavor that Lewis did so well. Moderns don’t seem to understand dignity and hierarchy. There is no scene where Caspian with drawn sword on his knees overthrows the bureaucrat of the Lone Islands, appoints a Duke and establishes justice. Queen Lucy, while the Narnians properly bow to her, smiles and tells her subject to call her “Luce!” The Captain at one point chides King Edmund for exceeding his authority: I was trying to imagine if any captain aboard a ship carrying, say, King William, would interrupt the resurrected King Arthur and tell him not to give orders.
Having Edmund regret his lost kingship seems (to me, at least) to miss the point and the greatness of Lewis’s conceit: his idea is that by being in king for a time in fairyland, you become more noble here, not more peevish.
But this is a general problem with Hollywood, which is built on notions of nobility that are made of tinsel and glass rather than silver and gold, and not something distinctively wrong with this movie. (Although I can imagine Lewis's Lucy being just as approachable as this version.)
(6) For me, the saddest loss in the adaptation is its failure to bring out the fact that Reepicheep alone of all the crew is not afraid to die, which is one of the most important features of his character in the book, a significant part of his nobility, and tied to his end. Perhaps this, too, is a Hollywood problem: it cannot convey, and perhaps most people in Hollywood cannot wrap their minds around, the possibility of someone seeing death for what it really is, with all of its sorrow and pain and difficulty, and having no illusions about it, and yet never fearing it. On a minor but related issue, I wish they had kept Reepicheep telling Eustace stories about the turns of Fortune's wheel; it would have conveyed more of the sense of what Reepicheep really represents. There was always something Boethian in Reepicheep's chivalry.
I am very much hoping that the movie does well enough that they do The Silver Chair; while The Magician's Nephew is my favorite of the books, the character interaction in The Silver Chair was always excellent, and it should be more easily managed for cinematic purposes.