6. Team Fortress
Why Its Controversial: Team Fortress's rise to prominence as one of the daddies of co-operative online gaming really is a story to behold. Originally beginning as a Quake mod, Team Fortress was the first class-based multiplayer shooter in which no class was superior to the other, and effective teamwork was the only way to win the day. For that reason, many classic Deathmatch players shunned it, at least until the point it went on to enjoy widespread mainstream success. Eventually, Team Fortress, the concept, was purchased by Valve and renovated, yielding Team Fortress Classic as a result and later, Team Fortress 2; a game that still enjoys an active community to this very day.
Why It Influenced Gaming for the Better: Deathmatch has been prevalent as a concept since the dawn of multiplayer gaming; players run around maps endlessly killing their friends before being defeated, only to respawn and begin again. However, Team Fortress placed a heavy emphasis on multiplayer objectives, such as capturing territory for example, and players were forced to rely on other team members (and the abilities their class provided them with) in order to survive. Team Fortress 2 still has a hugely active community and its influence can be felt in other games on the market too; take the Battlefield franchise for example, whose heavily TF influenced class-based, co-operative gameplay is arguably one of the reasons its CoDs biggest multiplayer competitor. Team Fortress might not be the greatest multiplayer game on the market by todays standards, but its certainly one of the early innovators.