I would have liked better blue or purple crystals, they are the most common crystals in nature, they look better and there's too much green in the game already.
So:
Crystalline - Green crystalline arms and chest.
Metallic - Gold arms and chest
Aftershock - No mask.
I don't like the no mask thingy, one of the reasons I don't like to play as Royal Storm Kitana or Deceptive Reptile.
EDIT: I see one of the pics has Tremor with rocky arms and masked, so it could be that the different arms are power ups instead of variation differences.