The wife and I saw this one yesterday. Wes Anderson FINALLY hit one out of the park IMHO. I do not praise too many romantic comedies, but this is a great movie, while remaining well outside of the mainstream of Hollywood productions. It is also the first acting credit for both 12-year-old stars, Jared Gilman and Kara Howard. I predict long careers for both.
Sadly "New Penzance Island" is fictional, there in fact is no such Island offshore of the smallest state, and the actual Block Island, RI does not even superficially resemble the terrain seen in the movie. However, the entire film was shot in various parts in the mainland of the state of Rhode Island, lending a unique look and feel to the production.
In an odd reversal of the normal order of things, the plot makes perfect sense from the audience perspective of a 12-year-old, while the actions of the adults seem unfathomable. The reviews I read before screening the film speculated that Moonrise Kingdom was partially autobiographical on the part of Anderson. This is actually foolish, as he was born and raised in Texas, four years after the 1965 setting of this story. Instead, the film Rushmore is partially based on Anderson's life.