Awwwwyes! I was so excited to see more Luna in the latest episode. She looks lovely here, I like the pose! You should totally make a sprite of the moon with Luna's head on it ala Sleepless in Ponyville, I think it'd be cool!
At first, before she directly made an appearance and started talking, I was quite annoyed, this was by the bit with her walking in the background. It was mainly because, in my stupidity, I didn't expect it to go anywhere, and, while I LOVE Luna, her presence has to have a point; she was a little shoehorned into the Canterlot Wedding episode, but she LIVES there, so she has a reason to be there. You cannot imagine how pleased I was when it turned out that Luna not only had a point to be there, but actually did more than sit around doing nothing (like Disney Princess Politics, for example).
So yeah, aside from one small plot hole, I can't fault that episode.