Best aesthetic, hands down. It looks great, and the little animations you've got on some of the monster boys are very effective at keeping it from feeling like battle of the static pngs.
Gameplay is nothing crazy, but it doesn't really have to be. I think both it fits surprisingly nicely with the theme, and does so in a way that I don't know that I've seen from other entries yet.
I'd love a full game with this vibe, but I feel like gameplay would probably need fleshed out a bit to hold my attention for too long. I don't know; if you have plans of expanding I'd be really curious to see what you did with it. Great work!