I won't pretend the episode is perfect. To me at least, there were two major problems: The first 3 minutes were too fast and I don't think we needed to see Celestia and Luna to be that intrusive with everything in that short period of time.
The second problem was the scene where Celestia and Luna just vent. It felt kinda out of nowhere and more as a convenience for the sisters to forgive each other at the end of the episode later. If that scene was basically these two sharing their own experiences from their own perspectives and getting mad because of disagreements, it would have been much better, less basic and more interesting.
But it's still a good episode. It's one of the best in season 9. And, at this point, that's what really matters to me.