The runes/swirls on the unicorn horn are a neat idea, especially if they differ from pony to pony, but they make it seem like a less natural part of the pony's body. Looks like it's been grafted on.
The pegasus having white/off-pink wings is an odd choice.
Fetlocks are alright; gives another avenue of expression for the character's design.
Colour schemes are quite nice, I like them.
Expressions are dopey as hell, but then again much of G4's marketing materials were dopey or outright uncanny so I won't make an issue out of it.
It'll be interesting to see how they move around; maybe G5 will have a higher animation budget rather than the Flash 'template' style we had in G4 (until the end when they went apeshit with the amorphous faces and whatnot).
How much do you guys wanna bet the unicorn has a name that follows the Sparkle formula?>Twilight Sparkle>Starlight Glimmer>Sunset Shimmer>??? ???