Solid game, I really like the simple but functional enemy design with their drops signalled.
Being able to restart with Space would be appreciated!
The core concept is great but it is very counter-intuitive how much not missing shots matter in the beginning paired with how wide-angled your shots are. I think the simplest way to improve this would be to add some negative vfx and sound to the shots hitting the screen boundary (ie missing), to make it obvious that this is something that you want to avoid more than anything.
Without knowing this it is easy to just stay in the limbo of shooting constantly and wondering why you aren’t progressing. Maybe you could take it further to explain this better and have the game play out inside the body of something that you want to actually preserve (for example invaders are coming inside the mothership and you have fight them there), so the screen boundary would actually be the walls of the ship you want to avoid friendly firing at, then it would make sense that if you hit the wall enough the whole thing blows up. This would solve the “limbo state” by progressing you towards game over if you aren’t playing the game right, as you couldn’t heal the mothership the same way you can reverse your own fever damage ad infinitum now.