I have seen this film 4 times at the cinema now. As an Aardman fan I desperately wanted to like it and wasn't quite sure how good it was the first time I saw it, but it is so packed with detail, ideas and striking images that I believe it repays repeated viewing. Obviously there is a problematic aspect to this though, which is that most cinema-goers will only go and see it once.
Perhaps for some people the film is not what they were expecting from a pirate adventure - these pirates are not exactly the swashbuckling, ruthless outlaws of popular fiction, although anyone who has read Gideon Defoe's books on which the film is based will have more idea what to expect. Also, as with "Wallace and Gromit in the Curse of the Were-Rabbit", the emotional core of the film is not so much in the plot, but rather in the relationships between the different characters.
Underlying the action of the film are moral messages, only subtly expressed - the middle of the film turns around "the danger of people only liking you because you're famous" (as Gideon Defoe puts it in his children's book version of the film). Ultimately, though, the mood of the film is more positive than this, the characters' actions and their consequences elevating romantic love above the love of money, and placing the value of true friendship above both of these. And I think that's beautiful.