Well, it scrolls. Diagonally. You can shoot things, and you can also land to pick up refugees who have been stranded on the planet surface. You can fly through buildings and things too, which can be rather unnerving. It doesn't look particularly impressive, but then diagonally scrolling games rarely do. So much effort seems to go into lugging the graphics across the screen that little things like sprite design and special effects tend to be forgotten.
The purpose of all this is to liberate the city of Xenon from the fiendish alien invaders who have moved in. Most of the original population has been evacuated, but a few key figures remain. These are the ones you're meant to pick up. As you're doing this the obligatory alien hordes arrive and float around taking pot shots at you. I endured it for about 20 minutes and then moved on to better things.