It's the first PreCure All Stars movie, that grand and increasingly unwieldy series that for years kept doing crossovers of all PreCures to date. (This first one only has four PreCure teams, which is manageable.) DX means "Deluxe", by the way.
There's a simple rule to decide whether or not to watch this.
QUESTION: have you watched all six years of Futari wa PreCure (Max Heart), Splash Star, Yes! PreCure 5 (GoGo!) and Fresh PreCure?
ANSWER = YES: it doesn't matter what I say here. It's a foregone conclusion. Wild horses couldn't stop you. Look at the time investment. Having watched those series' 292 episodes (and probably also the movies), you're probably at least some variant of PreCure fan. You'll thus, inevitably, watch this concentrated nostalgia hit and spend 70 minutes squealing about this reunion with Honoka, Nagisa, Hikari, Mai, Saki, Nozomi, Rin, Urara, Komachi, Karen, Kurumi, Love, Miki and Inori. Plus all their fairies.
ANSWER = NO: forget it. Not even if you've seen half of them. Put it on ice and wait until you've finished. The whole point of the film is to get emotional reactions from the audience at seeing loved characters again. If you don't know the franchise, you'll think this is a dumb, one-dimensional string of fights, fights, fights, fights and fights. It has a paper-thin plot and not much conventional characterisation. (Nozomi doesn't get a chance to be an idiot, for instance, although in fairness she does get a scene of optimism.) After all, these are fourteen variations on the same pure-hearted hero template, with most of the differences between them being cosmetic.
Much of the characterisation, in fact, is in the fights. Every PreCure team gets a big fight all to themselves, which is rare in the overcrowded All Stars films. What's more, everyone has their own combat style.
Honoka and Nagisa are pugilists, for instance, outdoing everyone else in sheer brute strength. (They also have overpowered magical attacks, but they're most famous for fisticuffs.) They punch an airplane out of the sky. I'm not joking. It's an evil plane. That's the most awesome moment in this film, although its most impressive single punch is Milky Rose making a crater.
Saki and Mai, on the other hand, are spellcasters. They can throw up forcefields to repel your energy attacks, then blast you with their own.
THINGS YOU'LL SEE IN THIS FILM
1. All the Yes! GoGo transformation sequences, in full. Including sodding Milky Rose. You could get up and make yourself a coffee while that's going on.
2. Honoka and Nagisa's marvellous screw.
3. A mildly eccentric attempt at a message. The PreCures are powerful together because they're all different, plus "all under the same sky". What's odd about this is how much it baffles the baddie.
THINGS YOU WON'T SEE IN THIS FILM
4. Cure Passion. The film was released on 20 March 2009, between ep.7 and ep.8 of the Fresh season. She hadn't appeared yet.
5. Any returning villains. All we have is mindless monsters (Zakenna, Uzaina, Kowaina and Hoshina) being resurrected by an energy-absorbing liquid supervillain called Fusion.
Is this a good film? Absolutely not, even though I loved it. Its plot is one-note and the baddie finale drags on a bit. However it's an All Stars film that feels like a proper crossover, with all four teams getting lots of screen time and cool fighting moments. It's not struggling to cram everyone in. Every team gets a big fight, accompanied by their own theme song. (Music is huge for this franchise. You can't not play the iconic songs. You just can't. This is a big music movie, both of old songs and new ones, like "Sparkling and Cute! The Great Pretty Cure Gathering" which would be used in different versions as the theme song for all three All Stars DX movies.)
If you love the characters, you'll love this film. That shouldn't surprise anyone.