a few observations

[irmen]

• the wave counter is a bit weird? or i don't know what it's counting exactly?
• is it on purpose that your ship keeps moving left/right even when you released the key?
• when sitting against the left or right screen border, your ship can't be hit anymore by the aliens it seems

[irmen]

more precise movement is possible by using the joystick instead of keyboard.
cx16.joystick_get2()

[cyborgar]

• the wave counter is a bit weird? or i don't know what it's counting exactly?

Yes, this is currently just looping over just two defined waves (0 and 1). I do need to create more waves with some gradually increasing difficulty (i.e more frequent bombs likely).

• is it on purpose that your ship keeps moving left/right even when you released the key?

Yes, I set a "delta" when left/right keys are hit. That way I don't have to worry about check for keys that are just kept pressed down and if "fire" (space) interrupts key signals. I will likely go back and check if I can redo this later. And possibly look at joystick support also.

• when sitting against the left or right screen border, your ship can't be hit anymore by the aliens it seems

Another one of these not quite complete things. I actually changed the size of the playfield a bit (reduced the sidebar with score etc) and haven't adjusted the movement patterns yet.

To be honest it's more fun working on the main gameplay elements than all the polishing and fine tuning, though it's that polish that that makes a game actually playable.