Cool concept and beautiful execution in the art/sound categories. The game itself is solid, but it feels sooooo sloooow. It feels like it would greatly benefit from speeding everything up and increasing the number of enemies faster. For the first two waves, it feels like there's no reason to even bother with the enemies.
You're absolutely right. I just didn't have the time to do balancing or a Boss for the ending :( Currently enemies are generated randomly based on some values for each wave, so sometimes it's super easy, sometimes its way too much. This should be solved with some proper level designing :)
The art/sound is not mine, it is from an old dos game called Tyrian 2000, which is awesome and I highly recommend you try it out, if you like plane scrolling shooters.
I know exactly what you mean, because I made the spawns in my game pseudo-random as well. It's very hard to balance in games like these. Made me wish I had time in the jam to script out an actual level with planned patterns.