Don't think there's any link to Monkey Island, actually, as the not-really-fearsome-pirate genre is quite established outside that game series. The film is based on a book. I haven't read it but it strongly reminds me of a children's book about pirates that I read once, at the recommendation of elTee (can't remember what it was called but hopefully eltee will come on here and tell me).
The visual style looks amazing. Love the combination of 'real' water and clay.