This is amazing, I can see the movement in the picture. The fact that you know how to use contrasting colors is a plus; I'm guessing you know a thing or two about color theory. I even like the way that parts of the picture are blurry so you can't exactly tell what's monsters and what's landscape allowing the viewers' mind to be creative. The composition in the final looks a lot better than the sketch too (I noticed you changed it around a bit )...Personally, I think it would be even more awesome if you would have used a little more(just a little) lavender undertones in the more yellowed-peachy areas that are further in the background, but it would probably change the feel of the piece quite a bit. The way it is now almost seems like a foggy dream, which is pretty darn cool. And I can actually imagine what all the people's emotions/expressions are just by the body stances (and they don't even have faces!!! ). So overall I think it's great! I wish I could do a real critique on this but I don't have the proper membership at the moment.. ... lol
The lighting is fantastic. I think my favorite part about this image is the dynamics of the subjects, though; the action in the flying bodies mixed with the ground erupting around the Hellions makes for an excellent take on just how horrid it would be to have those beasts blast through the surface of the earth. I like the sketchy feel of it, while you still managed to add tight detail to beautifully render the scene.
The color palette is great, as well; the earthy tones build up nicely, and the slight bluish cool accents add to that original buildup. All in all, a successful piece. I can see why Wizards had you do it.