Classic Game Mode – Natural Selection
I’m sure that a lot of you aren’t familiar with the Half-Life mod called Natural Selection. It basically uses the Half-Life engine to let you play an Aliens-vs-Marines type game. The Classic mode of NS pits the two teams against each other; the goal is to destroy the other’s primary structure. The Aliens have to destroy the Marines' Command Center, while the Marines have to devastate the Aliens’ Hive.
Sounds routine, right? Well it’s anything but... the fact that both sides play vastly different from one another changes things completely. The marine forces have a commander who can lay structures down that can be constructed by the players under him. The aliens on the other hand have no commander; each and every alien can evolve into different kinds of units – one of which can construct structures. To construct structures, both sides have to fight for and protect resource nodes, making the game revolve around laying siege on each other’s bases, flanking the enemy team, and so much more than your average multiplayer game. The short time I spent with NS was undoubtedly the most memorable of my multiplayer experiences.
i would have to say the Top 5 most played multiplayer game modes would be 
