In general, this free game is not unlike any other FPS (First Person Shooter) that has been launched in the last decade, with the small variant that it demands a set of system prerequisites that are much higher than those that would be really necessary for a game with the graphic quality that this game presents.
Wipe out all the enemies that you come across, and gather all the objects (they will come in very handy!). And once you have finished, you'll be able to sit back and enjoy the promotional video of Bulletstorm that has been included by the guys from Epic Games at the end of the game.
What are you waiting for? Download Duty Calls to your computer, it won't disappoint you and you'll be able to have a good time shooting at your enemies.