There are some really good and free games that we strongly would recommend.
One is: Wolfenstein Enemy Territory (a free) multiplayer first-person shooter video game; It takes place during the World War II. You chose side and what kind of skills you want, like engineer, medic, soldier etc depending what you chose thee will be some difference in what skills they have and what kind of weapon you can chose from, after that it is just to go out and shot your opponents. Download it here.