It's one of Ghibli's better movies. It's simple, it's charming and it's a breeze to watch. Personally I thought the ending needed another 5-10 minutes, but that's the nearest I have to a complaint.
The script's by Hayao Miyazaki and Keiko Niwa, adapted from a 1980s shoujo manga, but it's directed by Hayao's son, Goro. So far he's only ever directed two films and the other was Tales from Earthsea, which has attracted much scorn and won him a "Worst Director" award.
Fortunately, though, this was well received and indeed became Japan's top-grossing film of the year. (I'm not sure if that's domestically produced film, anime film or whatever, though.)
It's set in 1963. The old-fashioned school uniforms and black-and-white TV are an indication, but the real giveaway is the adverts for "Tokyo Olympics 1964". Our heroine is Umi Matsuzaki, a schoolgirl who helps to run a charming, mildly chaotic all-female house and gets praised for keeping the accounts in the black. (Dad's dead.) One day, she gets involved in student efforts to save a magnificently mad school building that's being used as a thousand clubhouses. (This isn't a fantasy film, but that building reminds me of Ghibli fantasies in its hold on your imagination.)
There's also a boy, Shun Kazama. They work together and like each other.
The film's almost that simple. There's some tragic family history that needs teasing out, which may or may not mean that Umi and Shun are siblings. (This isn't an incest movie, but just the possibility is too close for Disney and so from this film on, all Ghibli films have gone to GKIDS.) There are two interweaving plots, both extremely straightforward. The other involves the fight to save that dilapidated building and that's also pleasant and satisfying.
What's good about this film is, bluntly, that it works. Its narrative is alive and breathing. The momentum's gentle, but it exists and it keeps the film moving forwards. Ghibli films don't always manage that. Frankly, it's not a quality I associate with films written by Hayao. It's also full of charming music and little period details. There are people who've been a bit sniffy about this film. (One of them was Roger Ebert, so I'm not going to say these people are flat-out wrong.) Maybe it's just Goro's name. Maybe the animation really isn't as good as Hayao would have done. Dunno. Personally, though, I'm expecting the film to age better than quite a few other Ghibli works and to be significantly better regarded in twenty or thirty years.