Sorry I'm late replying to this comment, but most of those things you pointed out were plain laziness on my part.
The sprites are all mostly just circles downscaled in realtime by Unity's pixel perfect camera, and I wasn't bothered making actual UI sprites so I just played around with a few more circles. I would have actually sprited them if I had time to have a pixels per unit consistent with the rest of game, but sadly Unity's pixel perfect camera doesn't work for UI, so if I was to perfectly adjust each pixelized UI element to be consistent with the rest of the game it could just be screwed over by playing at a different aspect ratio than 16:9.
I've pointed out in other comments that the small window was just a dumb mistake on my part - I spent most of the jam playing the game in a tiny window and only realized later how incredibly stupid it felt in fullscreen.
As for enemy variety - this game ironically has the most enemy variety I've ever put in any of my games - fast blue enemies appear from round 6 onwards and slow projectile-shooting enemies from round 11 onwards. But naturally my difficulty-obsessed self makes it borderline impossible to reach those rounds (I haven't got to round 11 myself yet :-$) Sorry you had a bad time with my game!