I had skipped this when it first came out, having been less than happy with The Lion, The Witch, and the Wardrobe. But I'm half-planning to go see Voyage of the Dawn Treader, so I thought I ought to see PC, too. (Why? I don't know, exactly, it just seems that I should, but I guess that doesn't necessarily make sense.)
Depending on how generous I felt at the moment, my opinion of it could range from "not very good" to "really terrible." This Touchstone article by Steven D. Boyer covers a lot of the problems, focusing on the more abstract philosophical mistakes of the film. But I think those problems are the result of a fundamental aesthetic error. At any rate, the two aspects are certainly very closely connected.
Prince Caspian includes an attack on Miraz's castle, which as the Touchstone article points out does not exist in the book. It seems to have been invented partly for the purpose of showing what jerks Caspian and Peter are, and partly because the filmmakers believed they needed to have more big loud Hollywood action stuff than the book could justify. It was during this long scene that it occurred to me that the filmmakers were trying to turn The Chronicles of Narnia into The Lord of the Rings (movie version).
Well, it's totally wrong. I didn't think the Lord of the Rings movies were really very good, overall, as adaptations of the book, despite many wonderful moments. But apart from that, the Narnia books are vastly different from LotR. The world Lewis creates is utterly unlike Tolkien's. It contains little to none of the grand scale, the high and serious nobility, and the deep tragic sense of Tolkien's story. It's small and modest and homely.
Worse than that, though, is the intrusion of an immensely tiresome contemporary sensibility which has nothing in common with Lewis's vision. This is partly noted in the Touchstone article. My daughter Clare summed it up pretty well in an email exchange:
"Yes, injecting 'emotional realism' into a Narnia story is like putting giblet gravy on a cupcake. I can see what the director was trying to do, but it just doesn't work for Narnia. You can have either Narnia, where everyone (except a few select folks like Miraz and Eustace) is basically good and their actions are generally in good faith even if they're wrong, or you can have emotional realism, where everyone is deeply flawed and disagreements are often completely irrational. I mean, if it's all about the gritty realism, it's just not Narnia."
Perhaps the most telling example of the fundamental wrong-headedness of the film's approach is in the fact that it invents a romance between Susan and Caspian. Fortunately, they didn't go as far with this as they might have, but it was still a big mistake. Clare again:
"I thought they messed up Susan pretty thoroughly in the first movie. They were going for no-nonsense tough girl who can stand up for herself, I think, but the line between that and cranky troublemaker is very thin. On the other hand, I don't think book-Susan would put up with all the sighing and longing glances. She's always struck me a profoundly down-to-earth person - even if she did have some kind of relationship with Caspian, they wouldn't be all ostentatious and Epic Romance about it (more like the cab driver/king and housewife/queen from The Magician's Nephew if you remember them). It's almost like the director and screenwriters haven't read the books at all and are just working from a plot outline."
My emphasis above, because I think that sums it up pretty well. Susan is, in my opinion, as big an indicator of the fundamental problems as Peter and Caspian are in the eyes of the Touchstone writer. She's almost always sullen and irritable in what has become the pretty cliched Hollywood depiction of the Smart Woman Who Is Not Being Listened To By the Egotistical Males Even Though She Is Always Right.
I'm sure the filmmakers did read the books. The problem is that they decided to turn them into something they're not.