Technically, yes, this is a kids' movie, but it's much more adult than its predecessor. The actors have matured, their performances are better, and Edmund — who was always my favourite Pevensie kid in Prince Caspian — is easily the coolest Pevensie in the movie, too.
In The Lion, the Witch and the Wardrobe I very much disliked the casting of Georgie Henley as Lucy, as she was all pouty and big-lipped and snub-nosed and generally just oozed smarminess; in Prince Caspian, she seems to have grown into her role, and I didn't mind her at all — although that could be partly because she has a smaller role.
The highlight of the characters for me, though, was (not Ben Barnes, although I guess if I were 14 I'd probably be drooling all over him) Peter Dinklage as Trumpkin. Trumpkin was one of the best characters in the book, and in the movie he's retained all his saltiness with a little cute-sad expression as well in those big ol' eyes. Reepicheep, too, was pretty cool, although not portrayed the way I'd envisioned him.
There are huge plot changes, and the original story is completely altered. Most of the changes aren't too bad, although I preferred how the Pevensies met Caspian in the book, and disliked one of the battles the movie inserted. But the ending was better; for some reason the ending in the book always confused and bored me a little bit. Having said that, it's probably ten years since I've even read any of the books, so I guess I should really go back and re-read the series before I make any more book-movie comparisons!