I loved it, but only because I'm a fanboy who's watched all eleven PreCure series up to this point. I know all the characters, even the movie-only ones from other New Stage films. (Gureru and EnEn have become heroic fairies, while Cure Echo returns.)
Theoretically its plot's nearly as simple as the HappinessCharge movie (which I wasn't keen on), but...
(a) it's got 36 Cures, fairies, Monokuma-like giant teddy bear monsters, a villain and the son she loves. No plot can be truly simple with all that. Oh, and children everywhere are falling asleep and not waking up.
(b) the Land of Dreams is a new way to explore the PreCures and giving them something to do. Battles are fun (and they're here too), but trapping the Cures inside their dreams gives us little character moments. Nozomi (Yes!) is a schoolteacher. Saki (Splash Star) is running her family's bakery. The Fresh! Cures are winning a dance contest. Mana (DokiDoki!) is the prime minister of Japan. (I'd vote for her.) This is fun and charming, but also oddly powerful when it's Nozomi of all good, kind, scatterbrained people who eventually works it out. "This is just a convenient dream."
(c) the debate over Maamu's actions has some meat. You can't dismiss her viewpoint. Those children are indeed enjoying happy dreams, after all, even though promising to keep them asleep forever is sinister. Similarly, Maamu's protectiveness towards her son is all too understandable. She's a very believable mother, actually, e.g. when pointing out that Gureru and EnEn never came to visit.
Admittedly that's a rerun of the previous year's DokiDoki movie, but this version's better.
(d) GOOD FIGHTS. Everyone gets a spotlight moment. Splash Star are the flying ones. Milky Rose punches another crater. Even DokiDoki's Ai (i.e. the psychic baby) gets to defeat a volcano full of lava. Honoka and Nagisa simply deal out ultra-violence, but Moonlight and Cure Ace are impressively strong too.
(e) comedy. Hime graffiti-ing on Megumi's face made Natsuki laugh, while Erika will always be funny.
(f) "Could you go into Megumi's dreams to investigate?" This will have inspired doujinshi porn.
(g) Aida and Megumi look like twins in their civilian forms. (They're consecutive Pink Leaders.)
(h) Cure Fortune isn't in this film, because she was still hostile when this film came out. Cure Honey, though, makes a surprising little appearance.
It's pretty cool, but you'd have to know PreCure to get the full weight of that. The plot's quite original for an All Stars movie, with its dream-based story and the way our heroines don't want to beat up Yumeta. It turns the New Stage films into a proper trilogy, with links to both of its predecessors. It even has PreCures pulverising giant colourful versions of Monokuma from Danganronpa. (Monokuma is evil.) It's a good film.