I love how you're keeping true to the cannon art style. Well done. The light is coming from the wrong direction on Pinkie, though. I'm assuming the light source is Twilight's magic. If so, then Pinkie should be illuminated from her left flank, not her right-front.
Excellently done, but there's something that bugs me with this picture: you have Twilight beautifully done with the lighting coming from her shield and horn, yet you have the same kind of brightness coming from the left on Pinky. In this picture, it strikes me that due to the weather the only bright, direct light would be Twilight/her shield.
...Well, wasn't that a generic comment. XD Eh. I'm too tired to think out some complex critique or somethin'. Sorry... Truly though, this looks incredible, what with your amazing, simplistic style packed with its own flare. I love it!