It’s nice that you’re still working on the game! Can’t wait to see what will be in the full release.
I like the fire rate power-up, I wish you could keep it between the levels. I think the game needs some persistent ship upgrades, otherwise it doesn’t feel like you are progressing.
Sometimes I encounter strange black boxes in the levels, I don’t think they are supposed to be there. What could they be?
May I also suggest that you package the Linux version in a directory?
tar archives are usually created like this, and most people are already used to it. It can be annoying when your working directory unexpectedly gets cluttered by archive contents.
You are doing really well, keep improving the game. :-)