Arcades today are a hollow shell of what they once were. Game companies have been taken over by bottom-line-watching weenies who compete for your money by copying whatever was popular last year, as row after row of dancing, shooting, racing, and fighting games attest. But in the mid-'80s, companies tried clever ways to earn your quarters. It wasn't enough to copy what was popular; you had to make it better, or at least unique.
Exerion is a perfect example. It's a simple Galaxian-style shooter with a compelling twist: rather than sitting on the bottom third of the screen, waiting for your enemies to attack, you move around the entire playing field while flying across the ever-changing surface of a planet that unfolds beneath you.
Gameplay: Your spaceship is outfitted with two weapons: a single-shot, rapid-fire cannon with limited charges, and a double-shot cannon you can fire as often as you like. (Guess which one is more effective?) The action gets so frenzied that by the time you reach some of the higher levels, you may want a double shot of another kind.