One thing that FiM does exceptionally well, despite being a slice of life style cartoon, is grow their characters. Throughout the last two seasons and moving in to the third, we have seen all of the mane cast (well, most of them at least) evolve from the events that take place in their lives. Twilight Sparkle especially seems to be advancing in magic at a rapid pace. I remember back in the day when teleportation would end in her being dizzy and googly eyed. Now it's second nature.
AS we continue on, I'm sure we will see them evolve even more. Where would you like to see the ponies at in say, season five or six?