Let me just say: there was waaaaay too much singing! I mean, SIX SONGS in like thirteen minutes?!
Also: the cutie mark switcheroo makes no sense at all.
Cutie marks are supposed to be reflections of what a pony's meant to do in life, their TALENT, what makes them special. You can't CHANGE your cutie mark even if you become really, really good at something else and you know that THAT'S what you love?
This is what Magical Mystery Cure tells us: the cutie marks of six ponies were switched. Shouldn't that mean that their TALENTS were switched up, too? Aren't cutie marks there because of a pony's TALENT??
Say the answer was no. Say that the cutie marks were switched. Then: helloooooo, they are only IMAGES on the side of a pony's flank! Magical Mystery Cure is suggesting that the cutie marks are tied to a destiny, but apparently not a talent, because talents were switched up. How is that possible? It doesn't make sense. How can you be destined to do something that you have no patience for?
My second big objection is what followed the switcheroo. Yes, Fluttershy helped Rainbow Dash (that on its own is kind of surprising, because Rainbow Dash seems to be nothing but self-centered and arrogant). Yes, she realized she liked being around animals. How does that give her, her cutie mark back? How does that prove "the magic of friendship"?? You discover what you like - how does helping a friend get you your cutie mark back???? It makes no sense at all!!!
Okay, number three: Twilight apparently becomes an alicorn because she 'deserved' it - because she created a new kind of magic. Hello - she did not CREATE the magic of friendship - even if there was an actual magic to it. Wasn't the whole point of MLP that it was always there?
Plus, aren't alicorns immortals? Celestia and Luna are definitely immortal. BOOM, another goddess out of nowhere! And why so young?
That being said, okay, she was a gifted magic apprentice, so maybe she was always meant to be powerful. Her cutie mark does seem to be vaguely galactic.
Alicorn I can deal with.
But a princess?