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.
Because of how rushed it was to some people, some viewers question if Sunset Shimmer was really remorseful of her crimes and wants to be redeemed or was just faking it to gain sympathy and avoid any serious punishment. Given how she's characterized in the prequel comics, it honestly leans to the latter.
Anticlimax Boss: For a movie, you'd expect an epic showdown for a climax, right? Wrong.
Ass Pull: The climax reveals that Twilight doesn't even need the other five elements to be present to tap into their power; seems like the power of the bond Twilight shared with the human versions of her friends (and she's known these humans... what, like two days???) was sufficient to not only allow Twilight to reclaim the powers of the Element of Magic but also summon the powers of the other five elements... which has no basis in the show's actual canon. Sort of but not really justified by the complete lack of any explanation on how the Elements actually work in the show anyway, and by a Hand Wave from Sunset Shimmer that taking the Elements of Harmony into a world where they don't belong affects their powers.
Flash Sentry. Some fans despise him, believing him to be a Satellite Love Interest and plot-irrelevant, while others love him and his relationship with Twilight, to the point of putting together a petition for his pony self to appear in the fourth season.
Sunset Shimmer. Haters point to her stereotypical Alpha Bitch personality and lack of depth on top of it, fans point to her awesome design and the potential for her backstory with Celestia.
Broken Base: Fans were and are pretty divided over the idea of a High School AU and the simple fact of doing My Little Pony without the Pony. At the announcement, some were cautiously optimistic, others proclaimed it to be the worst idea ever, and some have just ignored it regardless. There's another, related divide over the character designs. This has not changed much with the release of the movie with opinions varying from "better than expected" to "generic and contrived". Since its release, fans tend to say that they're glad they saw it, but won't go out of their way to see it again due to being So Okay, It's Average.
Complaining about Shows You Don't Watch: Stuff like the initial preview, the movie poster, the first trailer, and even the mere description of premise caused some people to immediately complain about the movie without even watching the full movie itself.
Counterpart Comparison: Sunset Shimmer is more or less a combination of several villains from Friendship is Magic: Nightmare Moon (once close to Celestia, is beaten by the Elements of Harmony in the same manner, makes a Heel-Face Turn), Trixie (Evil Counterpart and foil to Twilight Sparkle, smug attitude, has Snips and Snails for minions, uses a magical artifact for a power boost), Discord (drives the Mane Six apart) and Queen Chrysalis (pretends to be respected member of the community, tries to discredit Twilight, transforms into a monster, brainwashes people, and plots to take over Equestria through military might). Elements of King Sombra can also be seen (conquering an area by force by casting a spell to enslave the local population, and both use the same black bubble dark magic effect in their spellcasting).
Die for Our Ship: A One-Shot Character? Having a canonical (if temporary) relationship with Twilight Sparkle? In a series as thickly saturated with shipping as Friendship is Magic? Yeah, poor Flash Sentry never had a chance. Hell, he was hit with endless amounts of bile even before the movie aired—before anyone even knew his name, for a picture of stock vectors of him and Twilight standing together—in what may be the fastest case of this happening to any character, ever!
Ear Worm: What, you think not having ponies means Equestria Girls can defy tradition?
So get up! Get down! If you're gonna come around! We can work together helping Twilight win the crown!
Fix it up! Yeah, it's all right! We'll get it ready by tonight! Mix it up! Yeah, help a friend! We'll come together in the end!
This is our big night! We made it happen, now let's party all night! We're here now and we worked so hard to make it come around to tonight, so let's try to make it last forever!
A friend for liiiife! That's what you are to meeeeeeee! A friend for liiiife! That's what you are to meeeeeeee!
Sunset Shimmer had a bit of a following prior to the movie's release due to the speculation fueled by her toy description and some fans were hoping she'd be the best part of the movie. Her popularity seems to have died down a little after the release of the movie (See below), but there's still plenty of fanart to be found of her.
Evil Is Cool and Evil Is Sexy: Her characterization aside, it's hard to deny that Sunset Shimmer's design is both these tropes. Her demon form is also the latter for some fans.
The thought of there being other mirrors that lead to different worlds other than a human world. Even as is, there's now an excuse for "Human in Equestria"/vice versa fanfics.
Both Pinkie and her Alternate Self know of the existence of other worlds, and it's implied they share some kind of mind link. The potential there is just staggering...
While it is very disappointing that Sunset Shimmer lacks a real character beyond being an evil Alpha Bitch, the potential for any story about her is staggering whether it's exploring her time under Celestia, the time between her leaving Equestria and the beginning of Equestria Girls, or the aftermath of Equestria Girls.
Similarly, those not turned off by Flash Sentry becoming Twilight's crush or his lack of character can now explore any potential backstory regarding him like what his relationship with Sunset was like before they broke up or explore his Equestrian counterpart's backstory or potential relationship with Twilight.
The existence of a Twilight Sparkle native to the human world.
The existence of other villains (such as Nightmare Moon, Discord, and King Sombra) native to the human world.
The identity of the mystery writer who sent Derpy the letter that made her blush has fueled endless speculation.
Girl-Show Ghetto: One of the many initial complaints was that it seemed "too girly" for some. What didn't help was that the first trailer seemed to enforce the very stereotypes that Friendship is Magic tried so hard to avoid. This was somewhat assuaged by the time the second trailer was released, though.
Now that it's been revealed that Spike is a talking dog, suddenly this video makes more sense.
Numerous fanfictions had touched on this concept before.
The movie makes a pretty big deal about Twilight having to get her crown back (which was more about getting back the Element of Magic than the crown itself), but the whole "You have to get your crown back!" plot seems almost silly when in the very next animated adventure the Mane Six return the Elements of Harmony to their source and Twilight just gets a new, presumably magic-less crown to replace the one that once held the Element of Magic.
Rarity tells Twilight "If I had a crown like that, I'd never take it off. I'd sleep in it!" In the Season 4 finale, we see Celestia sleeps in her royal regalia.
Jerkass Woobie: Some fans see Sunset Shimmer as this after her apparent remorse at the near end of the movie.
Just Here for Godzilla: Plenty of people only watched this to see what Human Derpy would look like. She literally does nothing but walk across the cafeteria halfway through the movie, then dance with a muffin at way in the back during the cafeteria song, and then again at the very end of the credits.
Normal Norman, the name of the guy with the knit hat and reddish jacket, partially due to that he lacked any obvious "cutie mark" equivalent for the human world. Also add that he's seen talking friendly with no less than three of the background female characters, suggesting he forgot to turn off his swag.
During the film's climax, a Wilhelm scream is heard, ruining the mood of the dramatic scene.
There's also Demon!Sunset Shimmer saying "spoiler alert!"
Pandering to the Base: Two different reactions came from the amount of Fandom drops that were in the movie:
The more accepting fans see the fandom drops as a great nod to them, and quite enjoyed moments such as the Cutie Mark Crusaders dancing to their theme song or the appearances of Derpy. They saw this as a way to Win Back the Crowd from the Audience-Alienating Premise, and plenty watched just for the appearances. As a positive review put it, the movie "Lets bronies know they were not forgotten."
The less accepting fans see the pandering as a blatant attempt to cover up what they perceive as bad writing, and feel insulted. As a negative review put it, "The movie has to jerk you off just to keep your attention."
Romantic Plot Tumor: Averted, for the most part, between Twilight and Flash Sentry. Even though they develop a crush on each other, the film never goes beyond that. They don't kiss, hold hands or say goodbye. They share one dance and that's all.
Flash Sentry, Twilight's new male friend, managed to become this before the movie even premiered! Some bronies are afraid he'll become her boyfriend. And if he does, may Celestia have mercy on his soul, for the shippers will not. Even some who aren't shippers feel he's a Romantic Plot Tumor, or just part of the High School Cliché Storm. Even aside from shipping concerns, a lot of people dislike him simply for being nearly irrelevant to the plot. There's only one scene in the movie where he's actually relevant (he finds photographs that prove Twilight didn't wreck the gym), and that action could have easily been given to anyone else in the cast. One of the writers confirmed he would have no future roles in Season 4, though fans are skeptical about that.
Sunset Shimmer also got some flack for almost the same reason people hated Flash, as they were afraid she would fit into the High School Cliché Storm as the Alpha Bitch, and some jumped the gun and predicted her to be a "generic villain with no clear motives". Things haven't helped a bit when the film came out, as she pulled off some questionable moves that would put her in the "no sympathy" zone (her bullying Fluttershy has been compared to Gilda making Fluttershy cry, for starters), confirmed that she is a generic villain with no clear motives (instead having the motives explained fully in the prequel comics) and an even more generic plot, and that her redemption either feels so forced that they're convinced that she's faking it, or that the punishment she received was a slap on the wrist. Either way, they're not buying her redemption. Hell, her characterization in the prequel comics shows that she probably isn't redeemed.
Ship Tease: What Twilight and Flash Sentry's "relationship" ultimately amounts to. He's a nice guy that she danced with once as a human and exchanged nothing more than a few words with as a pony. There's nothing to suggest that it will ever go beyond that. His pony self's extremely brief appearance in FIM have amounted to nothing more than a non-speaking cameo, by Word of God nothing more than a nod to the movie.
So Okay, It's Average: The general consensus appears to be that while the movie did turn out better than expected and is enjoyable (just look at the Moments pages), its not as good as some of the better episodes of Friendship Is Magic.
The background track that plays during Twilight Sparkle's football match against Rainbow Dash uncannily copies from Elvis Presley and his "A Little Less Conversation", referencing this commercial.
Daniel Ingram's remix of the title theme seems to be an homage to the remix by DJ Alex S.
Tainted by the Preview: The mix of leaks, Uncanny Valley promotional art, and rumors all before Hasbro unveiled of Equestria Girls in full left fans... uncertain about this extension, to say the least. The trailers convinced some fans the movie wouldn't be completely terrible, mostly by bringing it out of said Uncanny Valley.
The most common criticism is that the two new characters — Sunset Shimmer and Flash Sentry — come off as a little flat and could have benefited from more development or focus. Even those that did like them wish they were given more character and didn't adhere so much to their High School Cliché Storm roles.
Towards the end, Sunset Shimmer has a Heel-Face Turn, yet is still left behind in the human world by Twilight Sparkle and Spike, and we're not even told whether Sunset voluntarily chose to stay, or if she was left there as punishment. If anything, it just seems like a shoddy excuse to keep The Movie as self-contained as possible.
Sunset Shimmer's premise alone was wasted. Her being Celestia's first personal student (implying that Celestia intended her to be the bearer of the Elements of Harmony), though admittedly cliché, implies that she is Twilight's only equal if not superior in the magic arts... and she is introduced and reformed in a setting where Sunset and Twilight can never truly duke it out horn-to-horn.
And then there's the pony Flash Sentry, which we can assume would be characterized like the human, and could be an interesting addition to the mix of male characters in the show — and not going to appear in Season 4 as confirmed by the staffers.
Equestria!Celestia proved herself to be just Mr. Exposition and didn't do anything else beyond just dropping exposition, which also wasted a possibility of closing off the "former student" subplot that they made.
With the amount of makeup all of them sport (even Rainbow Dash and Applejack) in promotional art, the reed-thin bodies, along with the ears, wings and skin color they had as ponies, they look a lot like clowns. Or prostitutes. Or zombies. Zombie Clown Prostitutes. Fortunately they look better in the movie proper.
The prototype toys. Oh God, the prototype toys... At least AJ has her hat! The final versions of the dolls look slightly less like ass. Slightly.
These costumed characters meant to promote the movie, due to their face being frozen in the same creepy smile.
Anytime a character is given lips. Human lips just doesn't look right on an MLP character, human or pony.
Twilight Sparkle is using the Element of Magic, one-sixth of the most powerful magic known to ponykind, as a crown. And isn't even taking any security precautions. One character actually explains why it is so bad to lose it, but there isn't even a Hand Wave supplied for why Twilight has it out in the open.
The only time she leaves it in the open, she is inside of a royal bedroom, in the castle, with guards patrolling the hallway. She probably assumed that it was safe enough to leave it on the nightstand overnight. Which still doesn't explain what it was doing out of a vault in the first place, as they were stored there even when Celestia didn't think there were any threats.
Twight was keeping the elements for part of Season 3 after Celestia gave them to her in case Discord reverted to his old ways. She'd been keeping them in an unlocked glass case on the first floor of the library. Clearly the thought of thieves never occurred to Twilight in the first place.
Win Back the Crowd: The second trailer received more positive reception, and leaked camera phone images from the late part of the movie (from a 4chan'er who had to see the movie but had no interest in the show) further pushed some in the "win" column.
Even moreso with the toys, where the dolls are dressed in "sexy" outfits that not only are vastly different from the clothing worn in the movie, but are usually in conflict with the character's personality i.e. Fluttershy in an off-the-shoulder minidress.
Twilight Sparkle. It's bad enough that she's really awkward with her new body and doesn't fit in the school right away, but Sunset Shimmer makes things more difficult by uploading a video of her onto YouTube that makes her seem like she's mentally unstable... Or has a mental disorder. Basically, she's been cyber-bullied. In-universe.
Fluttershy. She's prone to this in the main universe anyway, but here it's shown that not having the steady circle of friends she has in Ponyville hasn't been good for her. The flashback to how Fluttershy got the Element of Magic involves her collapsing into a heap and crying because she can't get anyone to care about the animal shelter she volunteers at.