Really fun game, and honestly, I myself am always impressed when people do stuff witouth even an engine per say, let alone something witouth a library. (Altought me pretty dum dum, me don't really know the difference between engine and library 100%). and the visuals are also pretty good considreing they're all rendered up.
It's still super simple tho, so I don't have much to say about it sadly. Only thing I would mention is that, as someone else already pointed out, it lacks some difficulty curves, so it really stays pretty monotonous to play for too long. I kinda decided to spice things up by myself by doing tricks like zigzagging between bullets and try squeezing myself on the tinier bullet gaps whenever I could, but I still took very long to die even by playing like this, Altought thanks to that I can say that the ship controls super smoothly and I also had a lot more fun playing while doing shenanigans, so I guess that will be some extra points for it x)