Archive uses extensions not common in free zip implementations, 7zip can deal with it though. Game runs on Linux without issues, but seem to act weirdly in few ways.
* Sometimes I can't shoot while the last projectile long left the screen. Othertimes I can shoot the second it disappeared.
* The coins are pretty inconsistent to drop. Can take quite some time before you get enough for any upgrades.
* The acceleration on this ship feels kinda wild, but that was possibly an intention.
* If you click load next level in the store, you always get the first/same level loaded? I played for a while and it felt kinda samy every level until I noticed I'm still on level 1.
* Maybe start the how to play by actual instructions and put comments on how you made the game somewhere below or into credits or something. If I click how to play, I want to know how to play.
Otherwise nice idea, good execution.