It's a good thing this became available earlier than usual, since I'm heading to Magic Origins prerelease in a bit.
This story was very similar to the start of the Nightmare Rarity story in the comics. One thing the comic story did better is that the dreams and nightmares had more to say about the characters themselves. Given that, I was a bit disappointed by the first half of the episode. Well, OK, I suppose Fluttershy's dream reveals a lot about her, and Rainbow Dash's dream was fun.
That said, I enjoyed the second half a lot more, though I wanted to see even more of the characters getting creative. In particular, it was rather odd that Pinkie didn't do anything really weird. Big Mac turning himself into a princess was great in particular, along with giant Derpy.
As the episode was approaching the end, I was wondering if Tantabus would actually escape, which seemed possible given the title of episode 15, but no. I was also expecting Celestia to appear in the end, or at least in Luna's good dream, so I was surprised that she didn't. The reveal that Luna created Tantabus to punish herself was a direction I didn't expect the show to actually go in, and while I would have liked less of a sudden turnabout, it was handled well enough.
This feels like an episode that really should have been done in season 2 soon after "Luna Eclipsed"--or rather, both episodes should have been in season 1--but there's no helping that.
I enjoyed the episode well enough, but I feel like last week's episode would have started this sudden hiatus on a higher note.
Well, I suppose it'll soon be time to go back into the community thread, once fan art for this episode dies down. I'll probably still bump up this thread for news related to this season in particular. Discussion of Friendship Games will be in the community thread.
EDIT: Eh, thinking about it, that splitting of discussion was always due to Equestria Girls stuff happening after the season ends. Since Friendship Games is airing in the middle of this season, should discussion of that be in this thread?