The idea is pretty interesting, I like it.
Bullets are more useful when they are closer because you have more time to aim/re-aim them, so a slower bullets upgrade could've been nice. A 'universal bullets stay closer' upgrade would've been a cool way to let players specialize in a stat too, idk
I like it, the final boss was kind of a surprise, made me go 'oh yeah, that was from the thumbnail!'. Cool game!