In this game you have to stop the big grey block that slowly moves from the right to the left. You can do this by causing explosions with the colored blocks you fire with the five bars you have at your disposal. As soon as you use a bar, its power meter will go down. If there is no power left anymore, the bar cannot be used for a while, until its power has increased again. If you manage to push back the grey block completely, you will go to the next level.
Use the arrow keys (up and down) to change bar and the space bar to shoot.