Hmm, I had a rough time with this game, unfortunately.
On one hand, I thought that it was kinda cool to build up your spaceship, bit-by-bit, through killing enemies. The freedom in being able to add new modules onto your ship as well as upgrading them allowed for some great expression and customization. I also kind of liked the mystery of figuring out how the game works due to its minimalist design, like how money isn't represented with a number. Definitely some interesting progression to be had here.
But on the other hand, all of the progression felt ultimately pointless. All the game ever seemed to do was introduce more and more spongy enemies: they never fired back or got more complex AI patterns or anything to pose a threat, so what was the point of upgrading weapons in the first place if nothing provides a challenge?
To add to that, the core controls felt bad to me as well. Moving and aiming the ship was an exercise in frustration since you just keep flying to wherever your cursor is, never being able to stop and aim (and when you do stop at your cursor, you bizarrely do not point in your last direction, instead you always point to the right). Shooting being automated was annoying too: the constant drone of the same firing sounds going off over and over quickly became grating.
I can certainly see the appeal of these progression games and I think there is some neat stuff here, but the core gameplay here was a big miss for me.