It's nice. It's got a fun idea that makes for fantastic trailers. I really liked the ending.
Unfortunately it's also a bit slack and underwritten. It lost Misaki and Natsuki a bit. They started playing around. It's okay, but there's not quite enough to warrant feature length.
The premise ties into the series theme of books and fairy tales. Miyuki and her friends will visit a land of picture books and get involved in Cinderella (again), Journey to the West (aka. Saiyuuki, Monkey, etc.), Urashima, Momotaro and One-Inch Boy. (I knew about all of those except One-Inch Boy, but he's not hard to figure out. Besides, his quirk makes him the most entertaining of the five folk tales here. That's three Japanese folk tales, one Chinese and one that's best known in its Western form, but is actually far older and basically international.)
The guest character is Nico, who's arguably a reflection of Miyuki. She's a picture book character whose defining characteristic is that she always smiles and makes people happy. She also has rather wonderful angel-wings hair. Once upon a time, Miyuki made her a promise.
I loved the film's opening. Our heroines visit a picture book festival. Nico enters our world in a surprising way, then the PreCures visit hers. Everything's good... until each girl gets her own fairy tale.
This goes on too long. Smile! is a five-girl team, unfortunately. Four or even three might have trimmed the fat in this sequence. The film is too pleased with itself in mixing up the different fairy tales, with scenes that are individually fun but in combination drag on a bit. Furthermore, the film's not doing anything clever with the tales. It's just borrowing their imagery, really. Ep.39 of the TV series did more interesting things with Cinderella.
I liked the fairy tale villains helping the PreCures, though. The folk heroes get possessed by the Demon King, which annoys the villains who are now being neglected. Heroic villains are cool (and also oddly PreCurey, since they represent forgiveness and seeing the good in everyone).
1. this film might contradict ep.44 of the TV series. Each has its own flashback story to show how the timid young Miyuki became so happy and smiley. I think it's okay, though. Maybe they're both true? Miyuki might have drawn strength from both Nico's picture book and Granny's mirror necklace.
2. this was the first PreCure Series movie to top the Japanese box-office in its first two days of showing.
This isn't a bad film. However it's a bit thin once we're past Act One and it could easily have been a 24-minute TV episode. I think I'd have preferred that version. However the Nico-Miyuki relationship has emotional weight (despite Miyuki never really making amends for that broken promise). I also really liked the ending, with a non-fighting victory and an adorable fate for the Demon King.
That ending's so good, in fact, that I considered a recommendation... but no. The film's still a curate's egg.