You will be protecting the earth from countless waves of invading forces. You can use the arrow keys to move in the mouse to aim with the left click to shoot. The space bar will bring up the upgrades menu. There are an infinite number of waves and you will be fighting red tanks to begin with mixed with bombs. Some of the vehicles later on will be equipped with lasers and fireballs that you have to dodge if you want to stay alive. This is a mix between action and a strategy game because you must choose your upgrades wisely depending on your play style. There will be a lot of power ups available when you kill enemies to get stronger.