Well, compared to most shows out there, I think mlp has the most developed characters and stories. Everyone just seems so real in their personalitys and interactions that it makes it easy to relate to them. And aside from a few dark moments its nice to watch a light hearted show to get away from the other dark media were exposed to.
And yes, Rarity and Sunset Shimmer are amazing.
Especially Sunset, she's incredible.
(Art made by Galaxyart-Karl from deviantart)