What makes this story good is the small details the author throws in. One prime example is Fluttershy's mom, who has a very small part in the story. Many writers have made the mare an evil mother or disapproving. This story makes Fluttershy's mom Barricade, a giant (about twice as big as a normal pony) warrioress pony (she is head of the Pegasi Guard) who bellows out greetings and leaves every pony shocked.
She also loves her little Flutters and will defend her daughter when needed.
I don't want to ruin other surprises, but the author does well to make even bit characters feel real.