I received a bit more feedback about Alien Attack. Needed more depth for replayability / fun .
I added a mother ship in the background , and now there is a mothership boss battles at levels 6, 12, and 18 (final) .
Also some other features.
I hope this has added the needed elements to make it truly a good game. The using the shield (joy stick down) is useful for making it to higher levels.
I have used all but 11 bytes of the 4K ROM !
Video shows boss battle