For the cynical bronies, are Twilight's friends, brother, and mentor sincerely remorseful on what they've done, or is it a cover-up? Some people considered the former based on how things are in season 3, but for others who considered that the only person who apologized was Applejack and Celestia's form of apology can look suspicious, they tend to say they they are saving their own flanks. Conversely, when Twilight easily forgives them, is she being a true friend who'd rather Turn the Other Cheek than hold a grudge, or bottlingin? Or perhaps she took her anger out when she was fighting the Changelings, who turned into her friends...
Angst? What Angst?: Boy howdy does this get hit with a heavy amount, and don't think they get brought up in later stories because they're never mentioned again.
Shining Armor took being brainwashed by Queen Chrysalis, tricked into thinking that it was Cadance, shunning his own sister and indirectly leading to her imprisonment in the caves, and failing to defend the city from the Changelings until the very end rather well.
Heck, a lot of people took things rather well. Twilight took her friends, mentor, and brother shunning her even after she knows the truth behind the imposter rather well, Celestia took being fooled, her defeat, and failing to defend Canterlot rather well, and most of Twilight's friends took the revelation that they were fooled rather well too, sans Applejack. Heck, Canterlot's citizens seem to have taken almost being a happy meal for the Changelings and their city being invaded rather well. At least Cadance has an excuse to be happy.
The two-parter itself, some sees this as one of the highest point of the series. While the others hated it so much, that they ended up leaving the series.
DJ-Pon-3's eyes are revealed! ...as magenta, not red, and this was laterconfirmed by Word of God. Before the confirmation, some vehemently denied it, others assumed it was a trick of the lighting, others still supported it to the point of antagonizing neighsayers, and lastly, there were those who just shrugged and went "At least we know now."
Was the false Cadance being dumb by casually acting evil, like snapping at Twilight about her ruining her plans, having a brainwashed Shining Armor with Celestia being none the wiser, and singing her Villain Song in front of thousands of ponies, including Celestia and the ponies she fooled, or does it just fall under the laws of cartoon logic, Musical World Hypotheses and people should just relax?
Applejack apologizing on behalf for everypony, the other half sees that her apology itself as half-hearted and rushed with the others should be apologizing as well, and not just Applejack. Some see the others apologizing as irrelevant since Applejack was the one who told to leave Twilight, she should be the one apologizing as well.
It's hard not to compare Queen Chrysalis to Nightmare Moon. Both are black alicorns (well, the Changeling equivalent of an alicorn in the case of Chrysalis) with similar evil mannerisms and similar voices.
It's not difficult to find comparisons between the Wraith from Stargate Atlantis and the changelings. They're cruel and sadistic, they have forms of mind control, they're insect-based but look like their chosen food race, and they feed on sapient life forms.
There's her resemblance to Ursula; Villain Song similarities non withstanding, both of them hypnotize the male lead by disguising herself as his love interest, both are evil sorceresses, both are shapeshifters and are creepy and ugly in their true forms, and are plotting to take over the entire world and are powerful enough to defeat the rightful ruler of the land!
As could have been expected, this happened to Queen Chrysalis before the episode had finished airing, mostly because her Villain Song includes a line saying she's dreamed about this day since she was small, and because she has another line stating that she is pursuing her duty to find food for her subjects. This of course totally justifies the Mind Rape, the terror tactics, and the attempted invasion of a peaceful land. There's also the reprise where she says that "the day she has dreamed of" is taking over Equestria, not getting married.
A more justifiable example would be the rest of the Changelings; many fans believe they only follow their evil, sadistic queen for the promise of food; food which, however, they can easily see is composed of thinking sentient creatures.
Epileptic Trees: Some fans have justified multiple occurrences of the same ponies in a single setting in previous episodes as being Changelings.
Their Queen alone, being the latest "big villain" in the series, is sure to fuel tons of fanfics, much like Nightmare Moon and Discord before her. Not to mention the fact she's been beaten, but not sealed away or defeated once and for all.
There are already four groups dedicated to them over at deviantArt.
Also, both Cadance and Shining Armor. The former is a new alicorn and so origin stories and world building are inevitable; the latter is both Twilight's Brother and the captain of the Royal Guards. We may be looking at the Hero of Another Story.
There is a small upcoming of fanfics that call out the Ponies for their shunning of Twilight (or in some cases, Twilight for her jerkass behavior).
There are many "X is really a Changeling" stories out there, based on the premise of a given character being in truth a channeling in disguise and this being revealed to everyone during the episode's climax by the "love explosion".
In Western European mythology Changelings are creatures that are switched with human babies, not unlike the Queen switching with Cadance.
"Mi Amore Cadenza" means "My Love Cadence". However, they may be mixing up Italian with Spanish, since the correct Italian form would be "Il Mio Amore Cadenza", and the right Spanish form would be "Mi Amor Cadencia".
Arias are generally written for a solo singer, while "This Day Aria" is ostensibly a duet. The irony lies in the fact that the duet is between two characters, where one of them is in the guise of the other. Also consider that, excluding the reprise, the song was sung by the same voice actress Britt McKillip, making it still an aria for all technical purposes. So so many props to Britt for having enough inflection in her voice to make it very easy to distinguish between the real and fake Cadance.
Celestia has a Memetic Molester version of herself called Molestia, which started out as a succubus that took her form. Queen Chrysalis takes the form of Shining Armor's lover. Guess we know the identity of that succubus now.
Les Yay: After Rainbow Dash saves Fluttershy from the Changelings and picks her up, a kiss-like sound (most likely a "whoosh" sound effect for Fluttershy being lifted off the ground) is heard when their heads are closest together.
The scene where Pinkie convinces a changeling to mimic her ("Do me! Do me!") has been spread via the Changeling reinterpreting its Pinkie Pie guise somewhatdifferently.
Moral Event Horizon: Queen Chrysalis leaving Twilight imprisoned under Canterlot in caves no pony even remembers exist and she'll likely never be found, while taunting her sadistically about that fact. It's also more or less implied that she was taunting Twilight to get her to kill the real Cadance!
Most Wonderful Sound: Princess Cadance's singing voice. "For I oh so love the groom, all my thoughts he does consume...Oh, Shining Armor, I'll be there very soon!"
Narm: During the dramatic "This Day Aria" song, the reveal shot of Shining Armor's derpy Mind-Control Eyes may have caused a few unintended giggles.
Shining Armor and Cadance's slow dance. They're just sort of...leaning in and wobbling back and forth together, but oh Heavens, is it adorable.
You'd think Shining Armor's derpy Mind-Control Eyes would be hilarious and when seeing them in the initial commercial, they were but when put in context, it's really disturbing and depressing, especially at the end "This Day Aria" where the real Cadance cries as the mind-controlled Shining Armor approaches the altar with her fake.
Cadence and Twilight's Secret Handshake, which seems so much a cutesie shtick in the first part, becomes part of a powerful moment with Cadence desperately trying to prove her identity to Twilight in the mine, who was ready to kill her on the spot.
Princess Celestia being easily defeated, which prompts some viewers to see how useless Celestia was in the episode. Even though Chrysalis' powers was fueled by Shining Armor's love, and even the Changeling Queen herself was surprised for it.
Paranoia Fuel: The changelings, as the name implies, they can take the appearance of any pony, mostly your loved ones.
Ron the Death Eater: According to some fans, repelling an invasion that was spearheaded by the leader committing Mind Rape whose dream since childhood is to see Canterlot burn to the ground counts as unprovoked racist genocide against an innocent, peaceful race.
Some Anvils Need to Be Dropped: Works both ways: even if you're right, you need to gather proof and be tactful about it. On the other hand, no matter how outrageous or ridiculous someone's claims are, there might be some truth to it and find out yourself instead of jumping into conclusions.
Surprisingly Improved Sequel: "A Canterlot Wedding" is perhaps the only one of FiM's two-parters where the second part is significantly better than the first, since Part 1 was bogged down by exposition to establish who Shining Armor and Cadance are.
They Wasted a Perfectly Good Character: The two-parter was Princess Luna's only season two appearance beside her focus episode, "Luna Eclipsed". However, she only appeared for two brief cameos with lines in part one, and only returned for a single line of part 2, uttering only three lines in the entire two-parter. Some people got upset with Luna disappearing during the invasion, leading to multiple interpretations of where she could be, but most of them leading to the meme of "Luna is useless."note However, the previous episode already established that Luna isn't in Canterlot until nightfall in her cameo; she shows up in this episode only after the post-wedding party (which is occurring at night) began. This fact is often glossed over.
The cave scene at the beginning was also well done in terms of lighting and animation, to the point it almost looked like an Animation Bump to some fans.
What An Idiot: Chrysalis. She has just used the power of Shining Armor's love for Cadence to subdue Celestia, yet she scoffs when Cadence says that "[her] love will give [Shining Armor] the strength" to renew his repelling spell against the Changelings.
The Woobie: Princess Cadance. The poor girl was kidnapped and held prisoner below Canterlot while Queen Chrysalis was running around as her. She spends her Wedding Day locked in a cave underneath Canterlot. If the heartbreak in her voice as she sings her half of "This Day Aria" doesn't make you want to hug her, you don't have a heart!