Having watched the leak, I can honestly say that this episode was great.
- I love the continuity that the team is keeping from the premiere. It really looks like they are dedicated to this whole season long arc business.
- Pretty much each of the Mane 6 was in good form in this episode, and their interactions were very well done. Twilight was her usual egghead self, practically flipping her shit when she saw all the ancient books in the library and generally being the voice of reason for Spike. Pinkie was surprisingly decent in this episode, having some genuinely funny moments this time around instead of the forced #SORANDUMB moments that we've been forced to endure for so long. Rarity and Fluttershy were easily the best pair in the episode, with Rarity practically stealing the show through a mix of hilarious dialogue and "That's so Rarity" actions. And it was nice to see the return of competitive Rainbow Dash and Applejack.
- The overall mood and atmosphere of the castle was very well done. I would hesitate to call it scary, but the dark tones and random traps really added to the setting overall.
- Each of the ponies learned a very valuable lesson in not letting one's imagination get away from them. Nice character development.
- I love the idea of personal diaries for each of the Mane 6 as a replacement for the letters to Celestia.
- The very end of the episode where the "real" Pony of Shadows shows up (while predictable as all hell) leaves a lot of questions to be answered.
- The episode as a whole was pretty damn predictable. I knew Pinkie was the real Shadow Pony the minute I saw that the portrait's eye was baby blue (though I had my suspicions before that) and as I said above, I totally saw the very end of the episode coming. Regardless, I thoroughly enjoyed the ride.
- The story was admittedly pretty thin, though I suppose that left much more room for the character interactions, which were the highlight of this episode.
Overall, this episode is an easy 8/10, and my favorite episode of the season thus far.