The second of the Narnia films pre-supposes a pretty solid grasp of the back story inherited from the first film, despite subsequently heading off in new directions and introducing additional characters, and I confess that - perhaps because of my jetlag - the early going was something of a challenge as I tried to remember the series's mythology on the fly. The filmmakers clearly assumed that this might be an issue, since there are several expository scenes that regurgitate the key elements for our benefit, rendering the first half hour or so a little flat-footed.
The obvious point of comparison is with Peter Jackson's Lord of the Rings, which spent far less time filling in these gaps, though he had the benefit of a clearer narrative quest, whereas the Narnia saga takes place in distinctly different phases that no amount of scriptwriting ellipsis can avoid. Jackson's films rear their heads during the action sequences, too, since Andrew Adamson has clearly taken a page or two from his predecessor's book, though in truth recent CGI-rendered battle sequences are all becoming rather similar in their use of sweeping overhead shots of digitally clashing armies.
As you might expect from a filmmaker who cut his teeth on the Shrek franchise, Adamson sometimes seems more at home when dealing with the animated animal characters than with the human action. Individuals like the badger Trufflehunter and, especially, Reepicheep, a rapier-wielding mouse amusingly voiced by Eddie Izzard, are nicely rendered, and are also well-integrated with the "real" action. Reepicheep provides essential comic relief against a backdrop that is sometimes surprisingly grim, with the young humans involved in battles and political intrigues that push them to decisions for which they're not yet ready.