5. Team Fortress 2
Team Fortress 2 features the age old war of red versus blue, pitting two teams of players against each other in a battle to capture the most flags or destroy the enemy base with the detonation of a bomb-in-a-minecart, among other modes. Players choose from one of many classes, such as Sniper, Soldier, or Engineer, and contribute to the battle as best they can. Their contributions are made more diverse with the inclusion of character customization in the form of weapons and gear, which allows players to very slightly modify how they deal damage or perform in battle. You'll want to pay for the game if you want to further customize your character's looks.