I kinda asked this question already on #srb2pony, but "What made you interested or like MLP:FiM?"
And I kinda answered this question already, but for the sake of discussion... The simple answer is that I was willing to be open-minded, and then Prime gave it a try and rather liked it. He recommended it and told me that the characters were well developed. I trusted his judgment and enjoyed the series from the first episode.
Of course, that's not all there is to it, I'd given it some thought... because even from the first I'd heard about it, I could easily see myself watching this because of the way I approach some entertainment.
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My Little Pony: Friendship is Magic appeals to me because of the innocence it conveys without being intolerably condescending and flat like most children's shows nowadays.
It sounds odd, but the theme though cliche'd actually helps that immensely. Compare with Disney classics, Studio Ghibli masterpieces, and shows I grew up with like "New Adventures of Winnie the Pooh" et cetera... there is a sense of wonder and innocence even while conveying morals that while not subtle do feel that they come from the heart for the heart. I think that's where that "Disney magic" they love to talk about comes from.
Fact is, I appreciate such shows more now than I ever did back then. Society had taught me to be cynical, and the conflicts that surround us are always complicated... merely associating with some of them is soul-draining. I'm very nostalgic, and I think the reason why is because the more you have to lose as the world takes its hold on you, the more important it is to save something from it.
Because of this I embrace every new opportunity to enrich that part of myself... my options are fewer now that I am older and more critical, but the few that remain are worth it.
Someone I respect very much taught me the difference between a childish quality and a childlike quality. The former isn't always appropriate, but the latter can still be treasured, and can even compliment maturity. I learned this through experience, from people that have come into my life and have made a difference.