Destroy All Humans! is a humorous action game that pokes fun at the era of goofy 1950s sci-fi movies. The player takes on the role of Cryptosporidium 137, a Furon from the Empire who has been sent to collect DNA samples from Earth's inhabitants. With his advanced technology, including hypnosis and psychokinesis, Crypto can manipulate humans and objects around him. He can also use his Hypno Blast to control people and upgrade his arsenal with extracted DNA.
The gameplay involves completing missions, collecting DNA samples, and causing chaos throughout the city. Crypto can disguise himself as a human using the Holobob suit and abduct people or animals to add to the mayhem. However, he must be careful not to attract the attention of the authorities, including police, military, and government agents.
The game features different alert levels, similar to those in Grand Theft Auto games, which can make it harder for Crypto to complete his missions without getting caught. The player is constantly connected to the mothership, where they can purchase upgrades, save their progress, and receive new missions.