"Everything has to be made during the jam. This means you can't reuse any code or assets you made before the jam or from other sources"
I'm with you, fellas! :D
There are a lot of great games with very simple style, like just pixels or shapes. I believe you can make a dissent fun game without art skills :)
I also never made a full game. I generally struggle to make good art, learn Unity, and, last but not least, my English is BAD. But I always dreamed of making a game that ppl can enjoy. So here i am :p