Really ambishous for a game jam. Here's a couple of ideas I had (excluding those said previously) :
- Add a bit of post processing, vignette, fog, bloom, etc. It's an easy way to add a lot of ambiance and polish.
- Add a soundtrack, even if its just one song that loops. It can really help set the tone of the game.
- Add a bit of text to give some flavor and explication!
Keep on making games!