First things first: You, as the judge, decide the theme. Because you are the one to judge it.
Before I get to the second, good with the judging done, then we might be able to move on with this contest, so thanks for that.
Second: You really do need to select your words a lot better. There are many lines in that judging that makes me cringe, because it sounds, if not rude, then at least very blunt. I am all for blunt, but only if the blunt has a reason to be there.
Fine examples, as paraphrased: "You sketch is too sketchy", "Your perspective works as it should, and I don't like it", "The way you make the shadows work are correct for the situation, but I am going to assume it's unintended and you shouldn't do that", "Better position that smoke better, I can't believe it's coming from the building on fire", so on, so forth.
And one example in particular, because that was just some kind of burn:
Also looking at a few professionally drawn hands will help you understand the concept.
Yes, surely he does not understand the concept of the hands, rather than then not being particularly important for the overall work of art.
And third, because there's nothing like correcting people about your characters and worlds:
The angel boy (?) and human were a nice touch; they helped show off just how “new” the robot was.
I don't get how it makes it look new, really, but anyway. The angel boy would be the human, Cen. Yes, that is Cen, yes, he has wings now, at least in this case, white clothing is the Government uniform. The - human, is a Sururrian (doesn't really matter) named Kai. These are pretty frequent guests in my art thread.