Great game! Certainly has a lot of potential for a prototype made for a game jam.
Here's a couple things I noticed while playing:
1. The invulnerability time after getting hit is very short, meaning you can go from full to dead in the span of around 2 seconds if you're unlucky.
2. Certain enemies (like the triangle ships and those big circle things) can telefrag you very easily without warning. Maybe add a warning indicator for a second or so before they show up to give the player time to get out of the way?
3. It can be quite hard to tell when the free revive upgrade triggers as it just refills your hull without giving any indication of it happening. Maybe add a slowdown effect + some visuals before resurrecting?
4. For some reason, the in-game music seems to randomly stutter and cut out at times. No idea if it's a problem with my device or not tho.