A family with a group of kids goes on summer vacation when small knee-high aliens from outer space intent on conquering the planet take up residence in the attic of the home they're staying at. You play as the Zirkonians who have to prepare the Earth for invasion by activating a Sizematron device sent long ago that can enlarge the invasion force. In this action-adventure platform game based on the movie of the same name, you go through 15 different levels through areas such as the roof, attic, vents, living room, garden, and basement.
You can switch among 4 different aliens on the fly with different abilities such as one being able to double jump, and another can throw grenades. Along the way, you collect different parts with which you can use to make various weapons including customizable ones for use with the Wii remote. The aliens also can use special attacks such as Fingernail Slash Combo, Ground Pound, and Tornado Attack. There's 4 different difficulty levels to choose from.