This was surprisingly difficult, but I really enjoyed it. Was a bit confused at first, but after I restarted the game I figured it out pretty quickly. There were a few quality of life things I'd like to point out: the game doesn't restart after you lose, with no way to restart it (unless there was some other button I had to press?), the audio in later waves got SUPER loud when there's like 9 enemies on screen all shooting at the same time, and it's a bit confusing to figure out the controls when the 2 ships swap sides of the screen. I think with a bit of tweaking to the timing between waves (more enemies spawn even when you didn't clear the current wave), and some better AI (the enemies like to clump together, so it becomes nearly impossible to hit them), and some feedback on health (maybe scaling ship sizes to signify remaining health or something?) this would be really great. I honestly would love to play this co-op with someone, probably until I get mad at them for dying all the time ;)