This is an interesting adaptation of one of my favorite children's book series. It takes the first quadrilogy (the Mystery of the Tree House arc), but replaces Mummies in the Morning with a loose adaptation of Vacation Under the Volcano, which is unfortunate as Mummies was always one of my favorites. It also includes a really needless B-plot about a classmate of Jack's who has a crush on him and wants him to star opposite her in Romeo and Juliet (totally a play every third grade class puts on).
It also takes several other elements of the series and weaves them in - Peanut from the second quadrilogy, Teddy from Tonight on the Titanic, Merlin from much of the later series - which was enjoyable to see. It's not a precise adaptation of the books, but aside from the B-plot, it made perfect sense, and was a really charming throwback to my childhood. I'd like to see it dubbed and released here in the US for the children's movie market, but that'll never happen, given the level of violence in the Pirates Past Noon section (the pirates frequently aim guns at Jack and Annie, and at one point try to shoot them). Still and all, it's a nice throwback for American weebs like me who want to relive their childhoods.