Suggestion,
try introducting "power" mechanics very early to game, that will make player know there is actually something to look forward playing. I have to had a LOT of patience to figure there is actual such mechanics in a game, and otherwise game seemed like just most basic thing ever. Check game "Johnny upgrade" it shows very good example how your game could work much better if used correct way of level design.
For optimizing tips , you asked for inside "Is there anything you'd like the judges to pay particular attention to?" I don't believe anyone will have performance issues in such simple game? Computers are much more powerful than that, either you are trying to overoptimize or you made a huge mistake in logic where you call same script billion times for no reason. About having clean code, that comes with experience, just write more code.