An easy (though not entirely accurate) way of describing this film would be to call it AIR Lite. AIR the Motion Picture is a very simplified retelling of the television anime by Kyoto Animation, which is itself closely based on the visual novel AIR by Key.
The first thing you'll notice, assuming you have already seen the anime series (which I would suggest watching first), is a completely different animation style. This is because while the anime was produced by KyoAni, the film was produced by Toei Animation. Toei gives the film more of a visual novel look, but skips around between animation styles multiple times throughout the film. By that I mean, there's a main style they use for most of the film, but occasionally they use completely different styles scattered throughout. The next thing you may notice is that most of the cast has been cut from the film. All of the girls except Misuzu have been removed from the story. Haruko is still there, as is Kano's older sister Hijiri, the town doctor. Some of the other characters have brief, visual cameos, but the story only follows Misuzu and Yukito this time.
If you haven't seen the anime series, there are some spoilers in the film. So I would stop reading now if you haven't seen the series, and wait until I get around to reviewing that instead (or just go watch it!).
Yukito travels to a small seaside town, where he meets Misuzu, a high school girl working on a summer school project about the history of the town. Yukito plans to stay in town to practice his mysterious puppet trade during an upcoming festival, and Misuzu invites him to stay at her house with her and Haruko, as long as he helps her with her summer project. Interspersed throughout their adventures around the town (during which Misuzu exihibits the symptoms of a mysterious illness) is a story about a winged creature named Kanna and her bodyguard Ryūya. Misuzu is following this story as part of her project, because the story is woven into the history of her town and is the basis for the upcoming festival. As the two get closer, Misuzu gets sicker, the result of an old curse placed upon Kanna's race that causes them to die when they verbally express their love for someone.
Toei's animation isn't nearly as beautiful as KyoAni's in the series. The character designs have been changed (specifically Misuzu and Yukito), both visually and in their personalities. It's not drastic, but it's a difference. For example, anime Misuzu is far more childlike than she is depicted in the film. The curse and the story of Kanno and Ryūya play out quite a bit differently as well. In the film, there is a strong romantic relationship between the two, which doesn't really exist in the anime series. It's a good film, on its own; but personally, I prefer the series. The only real upside to the film is that it focuses only on Misuzu and Yukito, instead of having Yukito running around town and helping other girls. But it wouldn't be a Key game based anime series without those extra relationships. So my original declaration of it being AIR Lite is still a decent description. By cutting out 90% of the characters and their stories, the main story is much more simplified. But that's not AIR.
AIR the Motion Picture was originally licensed by ADV Films, but the rights have since transferred to FUNimation for any future distribution. I watched this in Japanese, but I did listen to the English version long enough to note that the same voice actors from the anime were used. So if you want the consistency...because the voice actor for Yukito changes in the Japanese version. Even so, when I watched the anime in English, I was really turned off by the voices and didn't think they fit the characters, so I automatically watched this one in Japanese.
This week's Bento Bako:
Vampires in Anime/Manga, part 2 (the...lesser titles)
November 2009 Previews selections