Moon Invaders

This was developed for a Ludum Dare "warm up" contest, where we had only 24 hours to create our game rather than 48.  I liked it so much I added many enhancements in the following week, and here it is!  The contest had 2 themes, 'moon' and 'anti-text'.  So this game takes place on the moon, and contains no text whatsoever.  Not even numbers!  It's in the classic Tower Defense vein, but with a dist…