Woooooowww, the

flow through me. I'm super happy about this episode, and nearly every episode this season to be honest. I mean, we had like, Castle Sweet Castle as our only average one so far? And it's not like that one was terrible. All other episodes have managed to pull on some manner of emotion. I'm really digging the trend of more mature morals, though I think this works best as the fifth season of this craziness. If the show had started like this, I'm actually not sure I'd have respected it as much as I do now, if that makes any sense.
I love that the ponies are a race who can't make sense of their world, because we as humans can't even make sense of our own. Too often in fantasy you have groups who are sort of passively treated in a racist way, because they are absolutely sure of their ways and behaviors and the way the world works in a way that no real society can be, as far as we know it. I think portraying a more "real" society, somehow, than the vast majority of make-believe races I've seen in other entertainment is a great achievement for the show and everyone who has worked on it.
So, the episode. I know we've seen stuff like this in other shows, but I'm not really a big TV person in general and might not get my examples right. Anyways, the fact we have enough of a mythology built up to even make something like this is astounding, and I think the fact that our ponies have come so far makes it feel more well-earned. Twilight herself reminisces about her own adventures for a short moment ("battled countless monsters, saved the world", something to that effect) in a way that makes her feel a lot older than she probably is. For her to have a nostalgia for these events in the same way she has nostalgia for what's going on during the episode makes her, much like in the Season 1 premiere, the perfect proxy for the viewer. This time though, she's not there to air the frustrations of someone cynical to the tropes of feminine entertainment, but to convey longtime fans' perspectives on the show to these characters who have been away from it for so long. I think it's a role that Twilight pulls off the best, and it's probably the best job-security she has insofar as proving herself to be the main character. She isn't meant as a vehicle for expressing the writers' thoughts, or an intrepid bystander, or a deus ex machina power-level war-machine. She's best as someone for the audience to channel themselves through, because this world is just as alien to her as it is for us, even with how familiar we both feel with it after over four years of fun and adventures.