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: MLP: Friendship Is Magic S3 E11 "Keep Calm and Flutter On"
Was Fluttershy pulling a Xanatos Gambit by assuming her loyalty to Celestia trumped her promise to Discord and she would have used her Element on him if he didn't reform?
Did Fluttershy really want to become Discord's friend or was she manipulating him to get what she wanted? Consider the line, "I'm just trying to gain his friendship any way I can so that he'll trust and listen to me!"
On a lighter note, does Celestia really have a use for Discord's powers? Or was she just using that as an excuse to try and reform him? (the season 4 finale confirms it's the former.)
The idea of an episode reforming a big-name villain like Discord had already split the fandom since the synopsis was first released. Upon viewing the episode, many felt that the ending was rushed, but fans are split on whether that ruined the episode or not.
Discord's last statement before being frozen again in "The Return of Harmony" was a sarcastic "Friend me". That's Fluttershy's plan this episode and it works. Discord even admits that Friendship is Magic. He also sarcastically states in "The Return of Harmony" that "maybe the magic of friendship can help you."
Fan videos involving Discord singing "You're Only Second Rate" are now all the more humorous at the lyric "Granny's gonna grab ya."
With regard to the episode itself, some were expecting to see Discord try juggling his usual chaos while still being Fluttershy's friend, perhaps trying to convert her to his way of life, but the story comes to an abrupt end instead of going anywhere with that.
Vindicated by History: Some of the flak toward the episode softened when the "Princess Twilight Sparkle" two parter showed that just because Discord is officially reformed, doesn't mean he's been nerfed in any fashion.
As of the Series 4 finale, we now know why Celestia wanted Discord reformed. That probably helps too.
Visual Effects of Awesome: Fluttershy's cottage rotating in midair so that everything is constantly sliding around. The attention to detail is stunning.