I loved this episode, although I must admit that the NO INDOOR VOICE AND SUPER FORMAL LUNA WHO SOUNDS REALLY SCARY was a bit unexpected. She seemed so sweet and shy in the episode we first see her, but then again, having your evil villainess persona just defeated would do that to you. We also see that Luna has a few personality flaws that she shares with Nightmare Moon, like being so quick to assume that the ponies didn't like her (although with them shrieking and running away, that's not so far fetched), and having to get her own way - declaring no more Nightmare Nights, ever? I suspect these weaknesses made her more suspectible to whatever turned her into Nightmare Moon in the first place, a thousand years ago.

(Yes, my image right now is of another Luna. Pure happy coincidence. :) )