Counter Strike: Source
Counter Strike was originally created as a mod of the original Half-Life, and has since expanded to become simply the most popular multiplayer game of all time.
Counter Strike takes upon the basic setup of Counter Terrorists (CT's) vs. Terrorists (T's) and pits them up against each other to try to win rounds. A round is won by either eliminating all of the members of the opposition, or by completing a specific task that vary from map to map. The most popular maps are Hostage Rescue and Bomb Defusal..
Counter Strike has progressed over the year, introducing new features and more maps with each newer version released. There was even a standalone game that came out in the form of Condition Zero, but it wasn't very successful.
About a year and a half ago, Half-Life 2 came out, and Counter Strike:Source (CS:S) was subsequently released; which operated on a new graphics engine. Shortly after this was released, SlingBlades started slowly making the shift to playing this game, seeing as most members were unsatisfied with the lack of competition in Halo.
We have been playing CS:S often ever since and have played in TWL and KW, posting more wins than losses in each league. We have since pulled out of competition temporarily.