The tears didn't come for me until the day after I saw it. I've been struggling with Seasonal Affective Disorder and an anxiety disorder, so this has been very rough on me. I'm getting better each day, though.
There's something I'd noticed about the series, though: Twilight and her friends have proven to be one of the greatest forces for good in the FiM world, connecting not only with other ponies, but also with other kinds of creatures. This was even true before Season 8 and the friendship school. What's astonishing about how much they're a force for good is that it comes not from their brute strength, speed, or magic, no matter how much of each of those they've got: it comes from simply being who they are---honest, loyal, generous, kind, funny, and friendly.
I'd always figured that the thing that gave Twilight and her friends the time and breathing room they needed was the fact that Celestia and Luna were running the country. And that, in turn, made me figure that Celestia giving her crown to Twilight would backfire spectacularly, keeping Twilight from being much of a hero by making her a bureaucrat.
But then I saw what Canterlot turned into after decades of Twilight's rule: creatures of every kind were in the streets and employed at the castle. That's something Celestia and Luna never managed, and hints that the kind of harmony and peace that she has managed to achieve for the world.
When I recorded my letter to Twilight, I said that she showed me how amazing it can be when a person or a pony allows themselves to grow, and really, her ascension to the highest throne in Equestria was the last piece of growth that she could've achieved, and now she's made Equestria grow, too.
Cadence was right in the Season 2 finale flashback: Twilight really is amazing!