These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Award Snub: Heartcatch Precure! The Movie: Fashion Show in the City of Flowers?! was nominated for the Kidscreen Award along side Zhu Zhu Pets: Quest For Zhu and Wapos Bay: Long Goodbyes. Wapos Bay won. No word, though, if it did better against Zhu Zhu Pets.
Ensemble Darkhorse: The fandom seems to have quite a fixation on certain supporting characters, particularly Sayaka and Kenji. The latter gets quite a bit of fanart of his imagined alter-ego from episode 21, Cure Fire. There's also a lot of fanart of his mom.
Germans Love David Hasselhoff: "Heartcatch Precure!: The Movie" was apparently popular enough in France that it was simple dubbed into French, and has a surprising number of Fans in the West, which begs the question why no Movie Theater/TV Station wants to air that anime film.
Launcher of a Thousand Ships: There is fanwork pairing up Tsubomi with every other Cure in the series, a number of supporting characters and a couple of villains. A few fans even joked that the series was actually all about her building a harem.
Les Yay: Tsubomi gets some in with Erika sometimes, and she still seems to have a crush on Itsuki. To say nothing of Yuri and Momoka...
Moral Event Horizon: Dune crosses this when he kills the Heart Tree, causing a worldwide near-apocalypse.
Most Annoying Sound: Tsubomi has an annoying cry when scared or upset, notably in "Heartcatch Precure!: The Movie!" when Olivier was leaving with Baroh Salamander.
Try watching episode 41 when you are in the supposed target age range. Because you are mean in class, your kindergarten teacher turns into a huge dinosaur with mean claws.
One-Scene Wonder: Keiko Ban, who so far only appeared in a single scene from episode 18 but has an oddly disproportional quantity of fanart.
Semi-averted. Keiko made a return cameo in episode 36.
Periphery Demographic: Adult males. Then again, given that there was a "marketing" paper that listed the "main target" as 4-to-12-year-old girls and 16-to-35-year-old men, this is an arguable subversion.
Yuri's meeting up with Cologne, her deceased fairy partner. Made sadder by the episode making it seem like he would be revived. Instead only his spirit appears before her.
As noted elsewhere, Dark Precure's death is also quite saddening. Many viewers are reported to have broke down in tears during this scene.
Tough Act to Follow: As stated above, this series in particular is considered to be so popular that the few series that come after to be not as good. Considering that until Doki Doki Precure came along, the ratings for the series in the previous twoseasons after heartcatch had a rather signifcant drop by comparison. It doesn't help that this series has some of the highest ratings in the franchises history, right after (If not up there) with the original series.
Throw the Dog a Bone: Infuriatingly denied. Even though Yuri has to cope with a machine-gun volley of traumatic revelations and events (her fairy partner dies forever; Saabaku is her father; Dark Precure is her genetic little sister and was created by her Brainwashed father specifically to kill her, only to die at Yuri's hands; her father leaves Yuri to comfort Dark Precure in her dying moments, her father is killed in front of her by the Big Bad) and still manages to save the world, she gets no reward or compensation for the losses she's suffered. It's an incredibly Bittersweet Ending for her character, extremely so by the standards of kids' anime.
Trailer Awesome Decay: Yuri's transformation sequence would have been much more badass and surprising if it wasn't the only damn thing shown in the next episode preview.