And You Thought It Would Fail: Many did. My Little Pony without the pony? High school setting with the cast as teenagers? Defying expectations, many did go to see the movies in theaters, and has made quite a lot of earnings for Hasbro. The sales have done very well despite the premise, and continues to be a very financially successful part of the line.
Angst? What Angst?: Sunset Shimmer seems to take being in a world where one of her natural abilities (unicorn magic) is nullified just from being there unusually well, even before she settles down and makes friends there. Furthermore, for a long time the series avoided talking about her possibly returning to Equestria, and when it finally does come up in Mirror Magic, it's treated like a plot point and Sunset shows no emotional reaction to going back at all, nor does she dwell too much on being back in her pony form.
Audience-Alienating Premise: Folks weren't exactly keen on the movie and the concept of the sub-franchise for quite a number of reasons, as many of the other entries on this page will go into detail on. It did well for Hasbro, though. This has since died down quite a bit as the quality of the films improved, but there's still fans who dislike the franchise, and some who have no desire of seeing it at all, or at least prefer it to remain a separate product; the "humans in Equestria" concept has always been a sore subject in the fandom.
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. He began to edge his way to Rescued from the Scrappy Heap once he got more to do than just be Twilight's love interest, but some of the early hate still lingers and induces groans whenever he appears.
The human Twilight Sparkle. Some are upset that her inclusion of the series has pretty much gotten the Equestrian Twilight Put on a Bus, as the human Twilight has much less Character Development and history than the Equestrian Twilight. Others like having the human Twilight around for her Divergent Character Evolution from the Equestrian Twilight and providing more options for story opportunities in the Equestria Girls world than the Equestrian Twilight had.
A related point of contention is Human Twilight's position in the hierarchy of the Equestria Girls; Hasbro seems indecisive about if Sunset or Twilight is the "leader" of the group, as various entries in the series have gone back and forth between them on this point. Some dislike Twilight being depicted as the leader since Sunset has gotten more Character Development compared to Twilight. Others don't mind since it matches the Equestrian Mane Six, and Sunset is still at least the Deuteragonist in regards to this dynamic.
Timber Spruce, introduced in Legend of Everfree, gets flak from some people for similar reasons to Flash Sentry, as Timber is viewed as another Satellite Love Interest, this time for Human Twilight. There's certainly more attempts to make him plot-relevant in his introductory movie than Flash Sentry was in his, especially in the climax. His only appearances outside of Legend of Everfree have been in the shorts, and even in Everfree, his character isn't fleshed out much more than "Twilight's boyfriend." Time will tell if any characterization outside of this gets brought up, but Timber is currently in a similar position to Flash Sentry after the first movie's debut.
Flash Sentry is a high school student wearing a t-shirt with a frayed collar, and his guitar is a Gibson Firebird non-reverse, a notoriously expensive and rare instrument that the typical working musician couldn't hope to afford in his lifetime.note The pony car he drives in the first film is probably more affordable than his guitar. His bass player has the bass variant, which is even more rare. Don't think about it too hard; maybe the animators meant to draw a Fender Mustang and Mustang Bass, which would have been another Visual Pun and much closer to a high school student's price range.
Sunset Shimmer has been shown to be living by herself in a two-story apartment complete with lavish decorations, including a few electric guitars hanging on the wall. How a high school student is able to afford all of this is never brought up, but it's never been plot-critical, and not meant to be examined that closely.
Counterpart Comparison: Sunset Shimmer has been compared to fellow Hasbro character Hot Rod, as a young new character who undergoes Character Development and takes over the position of protagonist from the previous holder. Bonus points for having the same red, orange, and yellow color scheme.
What happened to the native Sunset Shimmer? Fans assume she exists, but her whereabouts haven't been discussed yet. This leaves fans to fill in the blanks.
The idea of Sunset Shimmer visiting Equestria and/or reconciling with Princess Celestia has also been a fairly popular concept among fanfic writers. Such a thing would happen in canon in Forgotten Friendship.
Characters or creature from either world crossing over to the other is a concept begging to be written about.
"The Fall of Sunset Shimmer" shows Sunset being significantly older than Twilight at the time of her fleeing to the other world, and "Fiendship is Magic #3" shows the Sirens being banished to the modern Equestria Girls world from ancient Equestria by Star Swirl. Some authors decided to explore the implications of time moving differently between the two worlds.
A lot of stories explore For Want of a Nail ideas where Sunset's exile to the other world went differently in some manner, like someone going after her, her not going through the mirror and fleeing the castle to go somewhere else, etc.
It's established that Twilight didn't know of Sunset during their studies under Celestia, but nothing is said of Cadance, who was also studying under Celestia for years. A lot of fan works explore the idea of Cadance and Sunset's relationship in the years before Sunset fled to the other world.
A large portion of the fandom considers it as good as canon that Sunset was being groomed to be a princess by Celestia in the same manner as Twilight. Some go so far as to suggest Celestia was preparing her to receive the Element of Magic instead of Twilight, and/or that Sunset was her daughter (usually adopted but not always). Related to this, it's also commonly accepted that Sunset knew of Twilight during their tutelage with Celestia but Twilight didn't know her, and that jealousy of Twilight played a role in Sunset's Start of Darkness.
It's popular to depict Sunset as a vegetarian, keeping with her Equestrian heritage and the presumption that she wouldn't feel comfortable eating meat (especially since many of the common species humans raise for food are ones that are sapient in Equestria).
Ponified Human Twilight/Sci-Twi is near-universally portrayed as a unicorn like her pre-alicorn self. That her "ponied up" form has wings implying she's the equivalent of an alicorn is subject to Acceptable Breaks from Canon due to their feeling it's at odds with her character compared Pony Twilight and/or that she has yet to "earn" it like Pony Twilight, and Sunset Shimmer having done enough to be more deserving of it by now.
The premise alone would drive many fans of Friendship Is Magic to ignore its existence. Many have since softened since the series has improved in quality over time, and avoided affecting the show such that it could be ignored by those still inclined. There are still fans who prefer to imagine EG as non-canon, not because they dislike it but because they don't want aspects to be canon (for example Twilight visiting a human world, humans canonically not existing in Equestria, Celestia having a student before Twilight, Flash Sentry, etc).
In comparison to their canon (implied) Love Interests, Twilight x Sunset seems to become the more dominant ship within the Equestria Girls fandom for nearly every movie where the two girls get to share screentime, whether it's because of their Foe Yay looking interactions from the first movie or their Romantic Two-Girl Friendship scenes from the second movie and on.
Even that has its share of Ship-to-Ship Combat, as fans debate which Twilight to ship Sunset with. Some go for Princess Twilight, others Human Twilight, and some just say both Twilights.
In regards to Flash Sentry, many fans are far more accepting of him hooking up with Sunset Shimmer (due to the Fanfic Fuel regarding their history as a former couple and their interactions in later movies) or Derpy (often being by Flash's side, especially when he's being ignored by the other girls) than with Princess Twilight in spite of (or perhaps, because of) the heavy-handed attempts at turning them into a couple.
Germans Love David Hasselhoff: While generally well received (at least by the target audience and their parents' wallets) in its place of origin (after all, it did eventually grow into its own franchise for a reason), Equestria Girls just seems to have clicked better with some foreign audiences:
Latin America — Mexico in particular — is also reasonably fond of the series, what with them getting their own official musical theater version of Rainbow Rocks, courtesy of Tycoon Gounote A pretty big production company of theatrical, well, productions in Latin America.  — which started touring in Mexico and ended spreading southwards like an sparkly, colorful plague — reaching Panama, Colombia and Peru. And said musical production, which debuted on 2015, came back on January/February 2017 in Mexico — all this while having a very positive reception. There's also a lot of region-specific merch there, such as licensed Colombian toothpaste (which, naturally, include everyone's favorite shoddy knockoff products of dubious safety standards!).
Girl-Show Ghetto: One of the many initial complaints was that it seemed "too girly" for some. Ironic in that the show is just as girly, but had the benefit of three seasons of characterization.
Growing the Beard: After the first film got a lackluster response, Rainbow Rocks was a considerable improvement that helped Win Back the Crowd, and it's stuck through the rest of the series.
The franchise was created to compete with Monster High. And now Monster High has it's own counter-move with their Fright-Mares line.
A common fan joke after the end of Rainbow Rocks was that Human Twilight/Sci-Twi was a Mad Scientist based on her first appearance with a Labcoat of Science and Medicine. One of the Summer Shorts, released much later, is called "Mad Twience" and involves Sci-Twi engaging in some mad science to create a robot dog.
The earliest examples of humanized ponies started appearing in 2011 and a fan-comic that had some close similarities to the first Equestria Girls was started in 2012.
"Holy Shit!" Quotient: With the reveal of three Equestria Girls specials coming to Netflix, no one was expecting too much, especially after a leak of a song number from one of them. Then the synopsis' were revealed, and Sunset Shimmer fans lost their collective minds when one special promised Sunset returning to Equestria. The actual special took place in mostly in the human world, though, which completely negated all previous excitement.
The release of the book "Friendship to Remember" depicted Sunset Shimmer returning to Equestria and reuniting with Celestia, which is something fans have been wanting for ages. Then it was later revealed that this was going to be adapted into Forgotten Friendship.
None of the songs were dubbed in the Japanese version. Fans were not happy. While this was eventually changed with Digital Series, it doesn't change the fact that some of the most iconic songs from the first few movies are still not dubbed.
Try bringing up the topic of the human Twilight having wings in a fan forum. Bring a fire extinguisher or two. If you expect the idea of Sunset getting wings to come up, bring a dozen.note The major contention is that Twilight having wings implies she's an alicorn like the Equestrian Twilight, but the human Twilight really hasn't done anything to earn her wings like the Equestrian Twilight did. As for Sunset, the jury's still out on if she deserves her own wings or not, especially with the climax of Friendship Games. However, it's pretty universally agreed in relation to the first point that Sunset deserves wings far more than the human Twilight.
Just Here for Godzilla: The first movie had fans that were just in it for the background pony humanized cameos. After the first, several fans stayed for Sunset Shimmer, who had grown to be surprisingly well liked as the franchise's main protagonist. After that, many were also in it for Sci-Twi, While many fans do enjoy the series for its own merits, plenty in and without genuinely love these two.
Launcher of a Thousand Ships: As Sunset Shimmer made her transition into being a heroine, her shipping potential skyrocketed to levels rivaled only by the main series' Twilight Sparkle and Rainbow Dash. She been shipped with both Twilight Sparkles, the rest of the Rainbooms, Flash Sentry, Starlight Glimmer, Trixie, Wallflower Blush, the Dazzlings, and so on.
For the first film, Sunset Shimmer was a Base-Breaking Character at best, with most finding her a shallow and disappointing villain. Rainbow Rocks devoted an entire arc about her redemption and saw her become a Sixth Ranger to the group, and she became far more popular with the fanbase and subsequently became the franchise's Breakout Character, usurping both Twilights as the spotlight protagonist.
Flash Sentry is a slower, more gradual case. He spent the first movie as a Satellite Love Interest for Twilight that did little to endear himself to fans. As the series continued he got a steadily decreased role until he was slotted more firmly into the supporting cast, and began to show some more personality as a goofy but likeable Casanova Wannabe. The result: his reduced role cooled the hatred for him while the improved characterization he exhibits when he does appear has begun to win him some respect.
Self-Fanservice: Hand-in-hand with the normal show, the human characters tend to be depicted in fan works as much more curvaceous and beautiful than in the series. Sunset Shimmer in particular has practically become a sex symbol for the Equestria Girls franchise.
Slow-Paced Beginning: The first film suffers from this - as Twilight has to meet all of her friends again in the human world, re-establishing these characters that the viewers already know. Rainbow Dash in fact doesn't appear until nearly halfway through the film! The first film is also a rather mundane Teen Drama that doesn't introduce magic until the final act. However the Genre Shift to become more Magical Girl esque and introducing magical antagonists has proved successful.
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.
They Wasted a Perfectly Good Plot: The idea of characters from either world crossing over to the other has come up once. This despite the fact that the core cast in both worlds have shown interest in seeing what's on the other side, and at this point there's little reason why they couldn't.
Tough Act to Follow: Rainbow Rocks redeemed the franchise in the eyes of many fans, so the following movies frequently get judged against it.
When seen in animation, the cartoonier movements and expressions take the edge off of this trope. The increasingly fluid and improved animation and costume designs go even further to avert this as the movies go on.
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. Though some fans feel that Principal Cinch manages to be the sole exception.
Vindicated by History: The initial criticism of Equestria Girls describes it as another cash-grab scheme to compete with the successful Monster High series which started three years earlier. Fans have gradually warmed to the series and even believe that Forgotten Friendship is slightly better than the highly anticipated 2017 Movie.
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.