Like most arcade classics, Space Invaders's greatness lies in its simplicity. You move a ship at the bottom of the screen to the right and left, shooting at stacks of enemy ships that also move to the right and left, bombarding both you and the three shields you can duck behind. The ships slowly descend and if one reaches the level you're on, you lose a life. The more ships you destroy, the faster the remaining ships move, making the last few ships in any swarm very difficult to hit. As the levels progress, you'll face massive boss ships and may even unlock the hidden original arcade version of the game. New elements were added to the elemental gameplay, including power-ups and levels that play out on slippery ice, but the basic fun is still intact.