Sorta set inside a computer. With references to human evolution. With lots of strange graphical styles and funky music. And big big multiple stage bosses.
Gameplay is incredibly simple. Hold down fire and spray the crosshair over things to acquire up to eight targets. Release fire to blow those targets up. Press the other button to blow up everything on screen for a few seconds.
Very much fun. Famous for being bundled, in japan, with a 'rumble pack' attachment which you were supposed to attach to the controller.