Since my thread on BH hasn't picked up yet and I'm not the only one posting here I will just go ahead and say it was fucking amazing.
I went in fairly spoiler free if not completely, had no idea what to expect aside from the typical season premier shenanigans.
It was cool to see Twilight struggle with her wings and how her friends thought of her as being a Princess now and that she's "above" them so to speak and Twilight denying it.
All the backstory/lore if you want to call it that which we got was great too, we got to see where Celestia and Luna got the elements of harmony and how they were used versus Discord and later Luna as Nightmare Moon.
Discord singing winter wrap up was hilarious and the fact that he's still up too some shenanigans may end up with him being a sort of "Chaotic good" character now so he's not reformed entirely.
Twilight being forced to turn her back on her friends after they think she should go back and be a "Princess" for the sake of Equestria in case Luna and Celestia weren't found.
But then being "bullied" by Discord to go and help her friends despite the fact that if she died or something happened to her, Cadance would be the only Princess left in Equestria and that the people might loose faith in them if 3 Princesses went missing and never returned.
She basically showed that she's still the good old Twilight Sparkle (plus a pair of wings and a larger horn, giggity.) by turning her back on going back and sitting in safety being a Princess while her friends are risking their lives for Equestria.
It also showed that despite being an alicorn there's still things in the world that she can't quite deal with without the help of her friends, which really emphasises the "friendship is magic" morale.
Them handing in the elements of harmony back to the tree means that there's been more creativity for the writers/mane 6 in general to come up with other solutions that doesn't just rely on falling back on the elements of harmony to solve things unless it's really needed like locking Discord up again.
Also animations and lightning looked AMAZING, they have clearly put a lot of hard work into this season.
Voice acting was amazing as per usual obviously really talented VA's and John De Lancie returning in the premier already!
Season long story arc is gonna be really interesting to follow and see how the story develops over the course of the season and for as for what might be in the box? Or where, what or how the keys will be found etc. I ain't got a bloody clue, we'll have to wait and see.
Also Derpt spotted with an orange mane at the summer sun celebration just after Twilight does her thingy ma jigg.
(Just ignore Lyra looking like she's just smoked a fuck load of weed.)