This is a simple game where you dig holes and bury the aliens quickly.
Image Credit: http://www.handheldmuseum.com/CGL/EarthInvaders.htm
While this image below is not an accurate representation of the game
(don't have the CGL machine no longer),
it gives a good sense of what it might look like in Mode 1 (4 colours)
Of course there is no reason why we couldn't advance the design of the game further. A different viewpoint such as isometric might be a nice starting point.