Oh dear... the massive scale of this work is breathtaking.
There are only a few things I could think of that could throw us off a little bit.
See the soldiers on the very bottom right corner? I can't get a sense of depth on their head so their faces looks a bit like a man with a big fat upturned-nose.
And, if you look very closely at the changeling swarm in the background, I can notice repeated elements. Same leg poses, same leg shapes... Time constraints? Sure, but it's a funny observation.
I also wonder if white-colored highlights is the best choice as something in the back of my head tells me that it's wrong by principle. I see an orange-colored sunlight if anything, soo....
But mostly, they're probably little things that don't totally ruin this piece as the sense scale this creates is more than enough to make it one of the best fan art I've seen. If I can give a more useful critique, there's plenty for me to learn.