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.
YMMV: My Little Pony: Friendship Is Magic S1 E26: "The Best Night Ever"
Accidental Innuendo: While talking to the Mane 6 about places in Canterlot, Spike talks about wanting to show Rarity (who he has a crush on) the Crown Jewels
Awesome Music: "At the Gala," which seamlessly combines a different musical style for each of the mane six.
Ear Worm: At the Gala, in the garden, I'm going to see them all, all the birdies, and the critters, all the creatures big and small, we'll become good friends forever, right here at the Galaaaaa...! And that's just the beginning (Fluttershy's part).
Ensemble Darkhorse: This episode actually introduces quite a few new ponies, both named and background. A certain cello playing pony made her debut here. She has quite a few fans.
Fridge Brilliance: It's no wonder Celestia hates the Gala if she has to spend at least a good chunk of it as a door greeter.
And she has seen galas like this one for over 1000 years. No wonder they bore her.
Another example of how bad it is: in a fandom that loves giving antagonists the Draco in Leather Pants treatment, fanfic writers generally do the opposite with Blueblood, making him even WORSE than he is in canon (often depicting him as outright villainous), or only include him as a Butt Monkey on the recieving end of a Humiliation Conga. Exceptions exist, of course, but they're often deliberately written as subversions of the norm. Again, this really says something.
The Woobie: Really, Rarity when you think about it. The others messed up, sure, but after spending the entire season looking forwards and envisioning Blueblood as her Prince Charming, he treats her like crap and she puts up with it the entire night in hopes he'll turn out to be a Jerk with a Heart of Gold or she can change him for the better. While Rainbow, Applejack, Pinkie, and Fluttershy were at least partly responsible for their problems, Rarity did absolutely nothing wrong and still ended up getting treated like crap. It's rather hard not to feel sorry for her. Or cheer for her when she's eventually had enough.
It's hard not to feel sorry for Twilight Sparkle, as well. Her absence from the above "list" is noticeable; Twilight Sparkle may not have anticipated Celestia being too busy, but Twilight Sparkle stayed right by Celestia's side and behaved herself like a GOOD faithful student, standing there for two hours while Celestia did nothing but greet each guest! So Twilight Sparkle's right up there with Rarity in the "did absolutely nothing but got her evening messed up" list. At least she got what she wanted in the end, to spend time with the Princess.
Celestia herself considering that it looks like she has to spend every Gala as the door greeter for hours every time it's held for hundreds of years.
Or is she so utterly bored by galas at this point that door greeter seems mild in comparison to spending any more time than absolutely necessary in the company of her guests?
Spike as well, who just wanted to spend time with the Mane 6 and ended up drowning his sorrowsin doughnuts and cocoa at his favorite doughnut shop the whole time while they were all at the Gala. Luckily, that all gets straightened out after the Mane 6 join him over at the doughnut shop, not only to laugh away their troubles but also to acknowledge how in the right Spike was when he intended to hang out with them, especially after Celestia joins them later on.