Our "hero", Crypto 137, is back. Earth is under attack again in another alien invasion. The setting is now the 1960s. You go around hunting Humans with your Zap-o-Matic, Ray Gun, or brand new weapons. Occasionally, there are probing missions where you can hypnotize a Human to do something to carry out your plans for the Furon Empire. There are also missions where you trick humans into being abducted by your ship.
Crypto also has new weapons: the Dislocator, a gun that shoots purple discs and grabs anything (including tanks) to beat them up; the Meteor Strike, a gun that can rain down meteor showers upon the enemy... and another gun called Gastro, which is a hologram on a hovership that helps out Crypto.
The side quests have fleshed-out stories now; in addition, there are cult missions where you convince humans to worship an Alien God. A Co-op mode has also been added. The entire game can be played through on a split-screen and the second player can join in or out of the action at any time through the pause menu.