Planet Invasion is a straight-forward Defender clone. As in the original, you patrol a horizontally scrolling landscape infested with Praetorian invaders which you must shoot down with your ship. The aliens are out to grab the Caloxin crystals scattered on the surface. If a Grabber alien gets away with it, it turns into a nastier Killer. A third kind is the Chaser, which flies quickly after you if you wait for too long. Others are the Miners, which drop mines, and Beamers, which split into three Berserkers.
For a game for the Tandy Coco and Dragon 32, Planet Invasion scrolls very quickly, though the speed comes at a cost – the landscape itself is only made up of a dotted line. Apart from that, Invasion is fairly feature-complete, having both a radar overview of the level, hyperspace and a smart bomb.