Mostly, we learn that Twilight Sparkle thinks that she's living in a grimdark fanfic. From epic pony wars, to her excitement at fighting ancient evils from the depths of Tarteros, to her constant(ly disappointed) expectation that Celestia and her guards are strict authoritarians with tight security, she clearly didn't get the memo that she's in a children's cartoon.
But that's why we love her. Right?
This episode had a lot of highlights -- Pinkie Pie walking down the street without touching the ground, "That's Future Spike's problem!", Twilight not moving a muscle, "I thought we were doing this for fun!", "Happy Tuesday! Love your new manecut.", and of course, "I can't believe I just did that."
Rowyn pointed out that the spike/ice cream subplot was a clever way to avoid pushing the 'hakuna matata' moral into family-unfriendly aesop territory, by reminding you that actions do in fact have consequences.
The plot, though... I'm pretty sure everypony could see where it was going right from the start. Twilight totally should have gone back to warn herself not to let Spike eat so much ice cream. Also, time travel plots are boring, and stable time loops are the most boring kind (even if they make more sense than most of the alternatives).
But that didn't even come close to ruining the episode. I liked it a lot.
...I just wish I'd learned from Spike's example, and not eaten so much chocolate today. CURSE YOU PAST TERRYCLOTH!