Sewer Shark is an FMV-based shooter, and one of the first games released for the Sega CD. You move a crosshair around the screen and shoot targets. Occasionally, you can also choose to change directions at fixed points.
Of course the real attraction in a game like this is the story. In the future, maybe in the year 2000, people will be forced to move underground and live in tunnels. Unfortunately, these tunnels are infested with mutated rat / alligator creatures known as "ratigators." You are pilot of a Sewer Shark, a craft designed to navigate the Sewers and rid them of ratigators. It's a dangerous job, but if you clear out enough vermin you can win a one-way trip to Solar City and sunny beaches.