Twilight/Rarity/Rainbow stole the show, here. They were goddamn awesome in every scene they're in. The dragon costume was nifty and hilarious. I felt they genuinely cared and weren't just there for contrived comedy.

"Spikey Wiky" is perhaps the best way they can go about the spike/rarity relationship to keep it ambiguous; people like me who would find her behavior reprehensible if she doesn't share his feelings are pacified, as are those who'd be squicked out by the age difference.

Rainbow being worried about Spike being hurt was a good bit of characterization, I think. I raised an eyebrow because being concerned about being hurt is not something associated with Rainbow, but it's still something a normal person would see. She's not being flanderized, and subverted my expectation of her being such, which is good.

Spike had Applejack's blanket he got waaaay back in Secrets of my Excess. You can see it during his walking montage. That's more than a continuity nod, I think; it shows he's conquered his materialism without having to avoid gaining attachment to objects. It's a bit d'awww inducing too, since those gifts had meaning enough to him to take one with him.

World building is great! I heard some complaints that ponies not knowing about dragons didn't make sense, but it seems fine to me; Celestia probably knows a decent amount, but not the answers to Spike's questions. Also, all dragons so far have been shown to be fearsome, sentient, and keeping to themselves; mortal ponies probably wouldn't dare to go near them, or would be pushed away/eaten if they did try to research them. It also gives weight to Celestia's decision to send them up to the dragon in Dragonshy; most ponies probably wouldn't be up to the task (Daring Do is fictional, after all), but we've got the group that could stare down Nightmare Moon, and they're also in close proximity.

Also really liked the phoenixes. Not much to say about them other than the traits on display were pretty nifty and cool. Philomena was more annoying than anything; these are badass. Also, most birds would not take an egg back that fell out of their nest; them not taking back theirs either (we HOPE they wouldn't for whatever reason, anyway...) is more good world building, and shows they're not quite as sentient as ponies or dragons.

Did I mention Twilight/Rainbow/Rarity were awesome? They were.