Only three years have passed since the previous and first installment of The Chronicles of Narnia, but I'd hazard a guess that that's about two years too late for Prince Caspian not to fall a little short.
Cinema has been rather saturated by children's 'epic' fantasy films in the interim - Eragon and The Golden Compass most notably - few of which have lived up to the giddy heights of Lord of the Rings or Harry Potter. Although Narnia is lucky to have a highly recogniseable and marketable name, I think it would have done better to have been produced/released sooner.
Having said this, Prince Caspian is a solid, entertaining film, just like its predecessor. It just lacks that certain something that has made a franchise such as Harry Potter so successful. I dare say this is due to the rather less substantial story, but it's not all C S Lewis' fault.
There's nothing really that exciting about Narnia - yes, that battles are impressive enough and the landscapes breathtaking, but it's all so very twee. These battles needn't be blood-drenched, but there is a distinct lack of grime that makes it all a little too choreographed to be truly heart-stopping.
The characters are just as bad - lovely though they are, the Pevensies are just. so. boring. Edmund is the most interesting of the lot and he is sorely underused. Prince Caspian himself makes for wonderful eyecandy, but his dodgy accent and unconvincing angst don't help him rise to anything more than just that. The villains are suitably villainous but nothing we've seen before. Narnia does have talking animals which are convincing, at least - Reepicheep and Trufflehunter are fabulous (and are quite possibly more exciting than the children...).
But really, I'm nitpicking. Prince Caspian does what it should - it entertains. The film goes on for too long with too little to fill the time, but regardless it is distraction enough that certainly, for me at least, leaves a longing for a portal to appear to a magical world of my own. Of course, it doesn't really take much to get me wanting that.