I think the guy in the background needs a lot more orange highlights to really compliment the fact that he's breathing a napalm tsunami on the poor infantry bastards, and to go with that, a lot darker shadowing. If you colour some mild reflections in his breast-piece, that REALLY would catch people's attention.

I love the blood spray and bone-fragments off the dude's face, that's an awesome touch, and not just because I personally love gory scenes. The organic matter from his face and skull follow the path of the halberd quite nicely, I think. The chain-mail on the therapod is badass, nice work with the detail there, and the fire looks pretty good, especially the embers zipping through the air and the debris that has also been kicked-up by it.

I think you gave the armor for the two green-guys an excellent metallic touch and you pulled it off rather well; though it looks to me that's where your main focus was because the foxes on the left didn't quite get the same mastery that you gave the other.

I love this pic, overall. I think that if you gave the big guy in the back some more drastic shading to reflect the brightness of the flames before him, it would have got you a 5/5 for technique and impact. Great work!