The simple visuals are really good, it's very clear and is easy to read which is great for this genre of game. I initially thought the auto-fire was a bit annoying but when I say how many weapons were firing at low health, I'm glad it was auto-fire.
I think the game was a bit easy, it might've been a bit better to have less levels but more dramatic shifts in the number of enemies just to flow a bit better.
It'd be cool to see more enemy types, like a healer one which fires slow healing projectiles for other enemies but you can intercept them too. Or a quick to implement large cannon one.
Amazing job overall, the background and music were great too set a good atmosphere