Shoot waves of enemies that pop up on the screen and try to not shoot civilians. You get to select two weapons for each level and they are assigned to left and right mouse buttons. Then you click fire... a lot
Here I write what I think about the games I have played. The score is shown as a smiley before the title of the game.
Note about Movies: None of the Youtube movies that i link to are made by me and i include them only to give you a chance to see what the game looks like. Only the text and the smiley score act as my review of the game .