Planet 51 is a peaceful planet, with green undisturbed lawns as far as the eye can see, until the human astronaut Charles "Chuck" Baker lands on to the planet. Your task now is to use Chuck's robotic rovers as you play as his friend, a local youth called Lem, to repair his ship so that he can leave Planet 51. Throughout the game you have to explore Planet 51 as Lem, and learn to control various vehicles. Later on you can play as Chuck and Rover as well.

Whoever has played Simpsons: Hit and Run, can already get an idea of how the game is played. You run through a relatively free, open game world and do things for various clients. So in a way this is like a children’s version of GTA, except without all the killing. Initially your jobs include mundane tasks such as mowing the lawn, but as the game progresses things get more interesting and complex. In addition, each character has his own special characteristics. For example, Lem can move very freely, as he is a native. Chuck on the other hand is always on the run, and prefers to dive into trash cans to hide. Rover does what he does best; analyze rocks!

While there are some repetitive missions, the game does try to add some variety. There are several race and chase missions, which you have to compete again in between the normal missions. The vehicles range from bicycles to cars, which gradually become available to use. There also teleport stations which are scattered throughout the city.