I agree it is not too difficult to win. I built a flexible LEVEL and WAVE system. Each WAVE can configure formation and attack type, and all I need to do is add any number of enemies to the WAVE and then just add multiple WAVES to a LEVEL.
What this means is that its super easy to add new LEVELS. I ran out of time so I just focused on providing a working game.
Post jam I will add global high scores (ranking will be TIME) and add 4 more planets in the solar system, and the final Alien base.