The title screen makes it sound like you can expect an underwater-flavored ripoff of Galaxian, but it actually isn't very similar at all (unlike Attack Sea Monster, which is 100% an underwater-flavored ripoff of Galaxian). For one thing, your character is on the top, not the bottom, and you're not attacking a wall of aliens in the sky, you're attacking a sparsely-populated ocean of relatively random-moving creatures. Some move vertically and try to join you up top, which if memory serves, restricts your movement and makes the game harder. Pretty fun and looks nice on the FM-8, which doesn't have a tremendous library of nice-looking action games.