A great and very enjoyable double episode of the "high drama" type.
I loved the fact that we got several visions of the past; part of Night Mare Moon's backstory, in particular, a glimpse of Discord's reign and defeat at the hooves of Luna and Celestia, and even some new mythology/history, in the form of the Tree of Harmony. (I even caught on to the fact Twilight was having visions of the past fairly quickly: specifically, the moment that Celestia didn't interact with Twilight.)
Regarding Night Mare Moon in particular, there were rumors that she would make an appearance in Season 4. I said then that I hoped it wouldn't be "oh look it's time for Luna's yearly transformation again", and I'm very glad that it indeed wasn't (not that I expected much else). Whatever happened in the past is the past; Luna will never be Night Mare Moon again.
It was interesting how sudden Luna's (outward) transformation was. I never really thought about whether it'd be abrupt or gradual, though, and it makes sense for it to be the former. Celestia's and Luna's fight was quite dramatic as well, surprisingly action-oriented, but again that's hardly a bad thing.
Another thing I really loved was how they avoided using the Elements of Harmony to solve things again. In fact, I'm actually happy that they gave them up: not because I disliked them in any way, but because I think this is the kind of moving forward and actually CHANGING things that sets MLP:FiM apart. Furthermore, as Twilight observed, it's not the Elements that bound the Mane Six together: rather, it was their friendship, and that's something that'll never go away. All in all? My hat's off to you, Meghan McCarthy; you did a sterling job writing these episodes.
(On a side note, it'll still be my headcanon that the ponies themselves are the real Elements anyway, and that the necklaces were trinkets — powerful artifacts in their own right, granted, but not the be-all and end-all of it.)
Seeing Celestia and Luna perform the Summer Sun Celebration together was lovely, and Twilight added a very nice effect to it. On that note, I'm really glad they didn't go for another Sonic Rainboom again — that one is supposed to be so exceedingly difficult to pull off it's quite literally the stuff of legends, after all, and having Celestia basically order one for Cadance's and Shining Armor's wedding was already stretching it IMO.
Earlier in the episode, I was surprised Celestia and Luna don't appear to have any royal advisors. You'd think there'd be a council of nobles, royal magicians, viziers, that sort of thing — ponies who could have helped Twilight out after Celestia and Luna disappeared. The way the guards acted suggests this isn't the case, though. Curious, but perhaps immortal alicorn goddesses don't need advisors. (Or perhaps they exist, but the guards nonetheless recognized Twilight as the highest-ranking pony and thus turned to her for orders.)
The bit about the Mane Six deciding that Twilight should go back to Ponyville on account of being too important for Equestria to risk endangering was interesting. They had a point — but so did Discord when he got under Twilight's skin (and indeed, I'll say that as much as I understood Spike's suspicion of foul play there, this was one moment where Discord really proved that as chaotic as he may still be, he's definitely reformed now). In the end, I'm glad that Twilight went back, and I wondered just how the rest of the Mane Six were going to use the Elements of Harmony without Twilight's, anyway.
And it was nice to see Zecora again, but her potion was a bit of a deus ex machina. What was its nature? Was it just a general "vision" potion? What kind of spell did Twilight use to transform it — and wasn't it just me, or did her magic look fairly "dark" (akin to Sombra's) when she cast it?
There were more questions that the episode raised. Chiefly among them, why did Discord never mention those seeds when he got reformed? OK, perhaps since they never grew into anything, he figured they were dead — but that just leads to another question, why did they grow into something NOW? Did something else weaken the Tree of Harmony, sufficiently to allow them to bloom?
Also, what did the Tree of Harmony (nice, more backstory) give Twilight? Well, I suppose we'll find out the answer to this one soon enough.
I'm also still wondering about the nature of the Everfree. Given its name, I always took it to stand for raw, untamed nature: neither good nor evil but merely there, perhaps comparable to the Wyld in World of Darkness terms. Given that it was revealed that it was Discord's seeds that were responsible for the whole shebang, I'm still sticking with this, too: the Everfree may be dangerous, and maybe there be dragons, but it's not evil.
Good to see that Discord's still his old self — very much a trickster spirit, albeit not evil anymore. I otherwise dislike alignment in AD&D, but I think one thing they got right was realizing that lawful/chaotic is entirely orthogonal to good/evil; Discord is very much chaotic, but he's probably chaotic good nowadays.
There were no songs, at all! That's a pity, and doubly so after Discord lampshaded the "spontaneous musical number" spiel. On the other hand, the S3 season finale had enough songs to keep me mollified. :) And the background music was nice, of course, although I only really noticed it consciously when Zecora was speaking.
Luna and Celestia had very nice saddlebags when they battled Discord. Also, Sweetie Belle's scream is the cutest thing ever.
Regarding Twilight: her new tiara looks less nice than the old one. I'm not a huge fan of that pointy, jagged design. I also thought that she should've outgrown the whole "obsessing over lists and organization" bit by now, but OTOH she was right about not wanting to go on a stint to Ponyville before her duties were taken care of. Finally, I liked how she still needs to get used to her new wings and flying ability; it adds another dash of realism and depth to the show that she isn't just suddenly a perfect flyer the moment she grows wings.
I do wish Big Mac'd get more speaking lines than "Eyup" and "Nope". Sure, it's a funny running gag, but he shouldn't say these things unless it really makes good sense.
I did like the "
Rock-odile Cragadile" — we got Timber Wolves, too, so it fits right in. I also think this was another 3D-animated critter, which is neat.
I wonder how many cameos there were; I only really spotted Lyra. I'm sure there were more, though, not to mention other shout-outs and nods (like the brohoof).
And finally, it was nice to see Celestia again, especially when she first walked in on Twilight and Spike. She's such an amazingly regal character; I can see why everyone looks up to her.
The one thing I disliked? Not part of the episodes proper, actually: the various station overlays and logos. "TV Y", "CC", "Hub Network", "Play Pony Games Online", "Next: Littlest Pet Shop", "New Episode" and more — those were annoying. (I put up with them because I wanted to watch the episodes right away, though.)
All in all? Great season starter.
EDIT, 2013-11-25: I just remembered that Celestia also mentioned that Twilight's not her student anymore. It fits right in with her ballad in the S3 finale ("you've grown up, and your new life has begun"), but still, it was a bit surprising to hear it said so explicitely. OTOH, again, I'm glad the show isn't static: Twilight is moving on, as opposed to being stuck as Celestia's student for all eternity. And student or not, she'll still be the sun princess's protégé, not to mention friend.