I enjoyed this episode. I don't think it's the strongest season opener we've had, but it was a better than average episode.

A few random observations:

• The original princesses are barely even mentioned. I think the only mention was when one pony (it might have been Sugar Belle) asks Twilight if she's met Celestia. Normally season openers and finales seem to revolve around the princesses or prominently feature them. This episode broke with that.
  
• On a related note, in season 4 the letters to Princess Celestia were replaced by journal entries, but in this episode we didn't have a journal entry either. Maybe they'll return next episode?
  
• It is one of very few episodes where the Mane 6 don't entirely save the day. (Canterlot Wedding, The Crystal Empire, and Equestria Games are the others.) Instead a ragtag collection of friends from the village do — Sugar Belle, Double Diamond, Night Glider, and Party Favor — I wonder if we see them again? (I hope so.)
  
• Starlight Gimmer escaped. Just saying.