Fantastic Voyage is a first-person submarine-type shooter based on the novel "Fantastic Voyage" by Isaac Asimov. You are placed in a nano-craft and injected into an eminent scientist's body in a bid to save him from cancer. Your mission is to zap all the cancer cells while avoiding red blood cells, and white blood cells which will attack you.
The time limit is represented by gradually decreasing patient's health. Your ship energy is gradually decreasing too. If any of these drop to zero, you lose.
In addition to zapping cancer cells, you can also choose to zap red blood cells for extra energy (if you find yourself running low on energy), but at a cost to the patient's health and your overall score. Zapping white blood cells gets you a score penalty and decreases the patient's health, so the best policy is to try to avoid them.
The objective of the game is to complete the game (zap all cancer cells) with the highest score. As a secondary goal, the player can also try to improve his accuracy percentage.