I'll start with the music. This was the first time since season one I have thoroughly enjoyed - not just one, but several songs enough to want to listen to them again. Some of the others in between were nice and had their moments such as "Smile" or "Raise This Barn", but I never bothered to put them on my music player like I did "Art of the Dress" or "Winter Wrap-Up". Having so many memorable keepers in quick succession blew me away. Say what you will about the decision to make the entire episode a musical or the quality of work compared to other shows, but these numbers were almost all above average for the series itself and supremely catchy on their own. I had "A True, True Friend" stuck in my head after it ended (I like how they closed the credits with it too), and straightforward as the lyrics are, I feel they perfectly exemplify the true meaning of the show: That friendship is magic. It's especially great how they're delivered from one pony to another down the line.
Aside from that Mane Six standout... While the story probably could've done without "Morning in Ponyville/Life in Equestria" (the former of which felt like a slightly lame Beauty & the Beast parody but is instead apparently an homage to the musical Oklahoma!) it's a pleasant-enough tune and you can tell Twilight's VA (or whoever's singing, can never care to keep them straight) was trying hard. Surprisingly, I think my second favorite is the other group song, "What My Cutie Mark Is Telling Me". AJ's accent, fake or not, always makes me smile when she sings, especially during the "my destiny is nawt pretty" line. Pinkie Pie perfectly nailed her part - hearing her suddenly use such a nasty tone for "fix this busted water chute" was so surprising and really illustrated just how differently she might have turned out if she had stayed on that supposed "rock farm". I quite appreciated the nod to Pinkamena and figured my friend would too plus she'd surely ship Pinkie x Apple Bloom harder, but apparently she made no mention of it on her journal review. *shrug* Anyway, getting off-track, but it's those little canon throwbacks throughout the episode that made it really shine IMO. For example, mentioning the memory spell and Cutie Pox cure. As Celestia's walk through Twilight's hall of experiences (whilst describing her deeds through a beautiful ballad) shows, this was all about seeing how far she - as well as her friends, and the show itself - have come. We, including the viewers and the staff, have all shared in the story with the characters, and grown and developed alongside them. Sorry to sound sappy, but I think that's a message they were trying to get across.
Speaking of ballads, I admit I'm not as big a fan of the pop ballad used for Twilight's "sad song". The build-up was lovely, but the cheesy chorus kind of killed it (Twilight looked especially silly lip-syncing to the "Why-y-y-y"). It was cool to hear them try something different though. And the accompanying animation again did a good job of portraying just how miserable the others were despite trying their best at what they thought they were meant to do. (More on that later.)
The only song that really felt shoehorned in was the princess coronation one, but hey, at least Twilight was clearly as uncomfortable about the grandiose reception as we were. (Returning to that topic too.)
Not much to say about the animation other than it was good. They put some effort in at least.
Moving on to the biggest part: The plot.
First, pacing. I, for one, am happy with how they decided to handle it. Let's face it, haven't we had enough two-parters with epic first halves and disappointing conclusions? I am glad they chose to condense all the awesomeness into one, and thankful Twilight didn't spend an entire episode moping around instead of trying to find a solution. In that sense, she's actually light-years ahead of Pinkie in terms of learning how to deal with bad situations. We saw how she was using a breathing technique Cadence taught her in the last episode to keep calm, compared to Lesson Zero when she would freak out over something as small as being tardy. Even though she started hyperventilating when she found out they'd messed up, she still kept her head and helped lead the effort to correct the mistake. In this case, the fact that she realized the solution was so simple so fast is proof of character growth in itself - she has obviously learned just how important friendship is, not just to herself, but to everyone around her. Honestly, I thought the answer was pretty clever, and I commend Twilight for coming up with it so quickly.
As for the alternate universe, I felt what they showed us, albeit mostly through musical montages, was just enough to whet the appetite. The rest can be left to fanfic authors. (Heck, my friend just wrote and posted a Rarity one today, which did get me thinking a bit on the next topic so my stance may have changed slightly.) They revealed exactly what we needed to know: That the ponies' Cutie Marks were swapped and they're having trouble "adjusting" to their new lives. The fact that each member ended up with the job of another that they would most hate really works out wonderfully in the context of the story, and also acknowledges the established relationships between them. For example, making Applejack a dressmaker when she's repeatedly told Rarity she doesn't care for anything fancy is awfully cruel. Like Twilight said, it's different and IMO more interesting than when Discord altered their memories/personalities. It really emphasizes how each pony plays to her strengths (and not necessarily her species), as well as how much the town relies on all its citizens fulfilling their parts. Fluttershy is clearly out of her comfort zone trying to be a party animal like Pinkie, but the community needs a clown to keep them in high spirits. Before I never considered just how important her role is to the function of society. It definitely raised her a few points in my book. While I was worried at first how they were going to resolve her issue when all the others' marks were restored - and this is the only part I think was a little rushed - I think it's nice how it represented that every pony was in fact her friend. She doesn't need any prompting to be herself and have fun other than to make others smile, regardless of how well she knows them.
Anyway, this brings us to the subject of fatalism. I had a feeling it would rub some people the wrong way, but I took it the opposite. After all, isn't this episode all about arguing against doing something you don't like just because someone/thing tells you to? But I suppose the problem here is the concept of Cutie Marks themselves dictacting a pony's profession, to which I would say... Isn't it the other way around? I consider a Cutie Mark as a symbol of personal achievement - a sign that somepony has found his/her true calling. It's not like the Sybil System, to make a Psycho-Pass reference that would only make sense to Talon. Whether a consciously aware choice or not, I don't believe it's a brand a higher power suddenly slaps on you and you're stuck with it, but something that comes from within. Let's remember that even though Fluttershy was born a Pegasus, she was hopeless at flying and instead found she had a special gift for taking care of animals. Rarity did enjoy making weather patterns to an extent, but she just wasn't suited for serious forefacsting. Only when a pony discovers one's deepest passion does the mark activate to reflect both a balance between inner desire (even if not fully realized/appreciated at the time) and special talent, resulting in growth into a unique being. While one may argue this is an oversimplification of life, that people can and should have multiple interests, plus how can someone be so sure of what they want as such a "young" age anyway... Come on, this is a kid's show, don't think too deeply on it. Let's just accept magic is a lot better than, say, an aptitude test, at determining what's best for you. Ponies can of course have other hobbies too, nothing's stopping them from trying other pursuits if they want. Heck, who's to say a Cutie Mark can't be changed naturally on one's own over the course of adolescence, or even after one becomes an adult? It just probably didn't occur or even make sense to any of the ponies to question their so-called "destiny" when such cases of misrepresentation must be so rare, and in the end could only be caused by a spell. It's like if someone took away your degree (assuming it's already in whatever your actual favorite field is) and handed you a mop and broom, telling you that you always dreamed of becoming a janitor, that you've worked as one forever, and showed whatever proper documentation would be needed as proof until you were completely convinced. Even if you were terrible at cleaning, if you honestly had faith in your heart that this was what you were meant to do, wouldn't you keep at it - especially if others depended on you? Perhaps a better example would be swapping your preferred line of work for a dull office cubicle... Though you might feel confused at first and wonder why you went through all the training for a desk job that you hate, if you thought you did it under the impression you could do some good and really wanted it yourself... *shrug* Meh, I'm getting sidetracked again and not really sure where I'm going with this since there's no way to make a one-to-one comparison to the real world. Hence, fatalism in a fictional cartoon where everything is usually sunshine and rainbows shouldn't be taken too seriously. Point is, it's magic, and therefore it must be right. XP
So, this does segue into the most major development of the series... Twilight becoming an Alicorn Princess. Now, I'm gonna split the title into two and treat them as separate entities in outlining my points, so bear with me here. Will start with the Princess part first.
As deoxys's link to Lauren's interview showed, plans for Twilight to become Celestia's successor were already in place early on (though she's also gone on record saying the direction the studio has taken isn't what she had in mind originally, presumably referring to the Alicorn evolution - another reason why I'm addressing it separately), so I don't see where the problem is here. Celestia has obviously been training Twilight to take her place, and has put a lot of trust and expectation on the talented filly. While Twilight likely has every right to refuse the responsibility should she feel it's too much pressure and would rather stay in Ponyville with her friends (a process I can see happening if they do decide to retcon it), I'm sure she doesn't want to disappoint Celestia and seems up to the task. As for earning the position, I'd say she's already proven herself quite capable at this point. Like I said, this show revolves around friendship, and the fact she was able to not just create new magic, but recognize that friendship can create magic in itself, is the genuine achievement here IMO. She didn't try to take on everything by herself, but instead guided her friends to find their own way by allowing the bonds between them to break the spell. Before when she had to remind the others of who they were after Discord altered their personalities, she fought for each pony's friendship all on her own (the others just helped her capture/hold the next one down so she could cast the memory spell), and while that was all well and good... I think this was an even bigger act on her part to step aside and let others handle what she knew they could beat without "book magic" by thinking of not just her, but each other. To watch over the well-being of those she cares about without interfering too much, but using her wisdom to aid when necessary... That I consider a sign of a great leader. It's not just about her and the friendships she's formed, but learning to humbly accept she isn't almighty, that even though she's screwed up, she doesn't need to fix it all by herself. She respects that her friends are also individuals who can fend for themselves, so long as they get a little push in the right direction. Sometimes she has to be the one to give it, but once the chain reaction starts, anyone can take on the mane character's mantle and be a hero to another, someone they may love just as much as she does.
"Well, what if the power goes to her head now?" I hear the angry bronies cry. "What if she starts to snub her friends?" Please, she isn't Rarity (and even she sided with those "common country ponies" when it came down to it). She's still the same old Twilight. Didn't you see her jump out of the carriage to walk beside them at the end? Besides, this could present a perfect opportunity for a story lesson about balancing princessly duties on top of her studies while finding time to hang with her friends. Sure, it's been done before even within the series, but it doesn't hurt to revisit from another perspective. As for her friends bowing, Talon and deo already dismissed that above, but coming at it from another angle I can also see a possibility of them getting jealous of Twilight's success (again, Rarity already did that with Fluttershy in one episode, but just covering all bases here). And hey, this is Twilight we're talking about. She'll find a way to come out on top - no, to stand by her team while maintaining order. There's a lot of potential for new progress here as well and good examples to set for young girls. If they say it's not about becoming a princess for the sake of frills and servants and tea parties, then I will trust them on that. I'm curious what kind of canon mythos they'll craft around being a ruler who carries the weight of not just her friends or even Ponyville, but all of Equestria's citizens on her back. And like I said, if they were to retcon it, I could see her choosing her friends over the throne.
Now, for the Ursa Major in the room... I went into the episode knowing about the Alicorn transformation from deo's previous spoiler(s). I was fairly ambivalent on the subject, though I was a little concerned how they would introduce it - thankfully the episode utterly swept away those fears. I won't say I'm totally in love with the idea itself (and tbh the only part I didn't like was how Twilight boldly spread her wings with that high and mighty expression, but eh, minor nitpick), but I am okay with it. Going back to the fatalism thing, it is a bit awkward how she wasn't asked for any agreement beforehand, but that's Trollestia for you? *shot* And hey, at least Twilight seems cool with it because this is a kid's show who cares about the details of course every pony wants to have wings. I'm not sure what people are expecting to come from her being an "overpowered Mary-Sue". She could already use some highly skilled magic that the writers would have come up with to suit the situation anyway, she'll just be able to do more of it?
I would like to discuss the issue of immortality though, since I've seen it come up elsewhere. This is just a theory I'm throwing out there to hopefully make things a bit easier to swallow, but perhaps Alicorns aren't immortal, and in fact every creature in Equestria has a really long life? I mean, these are magical equines we're talking about, including Pegasi and Unicorns. Heck, they're practically ageless already, being perpetually ponies for some reason. Then again there's Granny Smith... Although come to think of it, wouldn't her being centuries old explain a "continuity goof" where she claimed to be part of the founding of Ponyville but Winter Wrap-Up stated magic hasn't been used to clean up winter for hundreds of years? (Note that I don't actually remember these things, I'm just looking stuff up for evidence as I go along.) So we might not have to worry about Twilight watching her pals grow old and die before her.
At any rate, this is all just dumb speculation and unnecessary since once again, this is a kid's show. They are writing for the initially intended audience, not to please us older fans. I would be amazed (and also very impressed) if they actually dealt with the topic of death. But I highly doubt it.