In the original two-parter episode, Nightmare Moon was spooky, loud and vindictive, with a tall figure, a black coat and a starry mane, while Luna was cute, shy and lonesome, with a comparatively short height, a blue coat and a light blue mane. This left fans debating how much, if at all, the two of them were the same character.
When we rediscovered the princess in Luna Eclipsed
, she was both cute and spooky, she hid her shyness behind a loud exterior, her estrangement brought her to fits of outraged anger, she had grown to an intermediate height, her coat had turned dark blue and her mane had retrieved some of its ethereal properties. The episode had Luna learn that she could be loved for being Nightmare Moon, or at least the holiday version of her. It all seemed to scream at us that what we had seen before was two extremes of a complex personality. And the whole did prove to be greater and better than the sum of its parts.
The second story arc of the comic book series, spanning from issue #5 to issue #8, takes the complete opposite route. We learn that Nightmare Moon is a demonic spirit of fear with a separate existence, this time possessing the body of another pony, while Luna herself seems entirely based on her brief season one appearance, with only occasional nods to her later episodes. This leaves Nightmare Moon without motive, her host's insecurities being only a mean to her control. Meanwhile, Luna is guilt-ridden, presumably over failing to stop a menace rather than over personal misdeeds. Thus, the arc uses a generic villainess and a generic heroine in place of an atoner. It is all a huge step down from everything that made Luna such an interesting character.
Broken headcanon, aw boo hoo hoo!
Alright, alright, there is a lot more to this arc and it is actually quite good. But I stand by my points.