The Best is Getting Better
Counter-Strike swept the PC gaming community in the late '90s as a mod for Half-Life. It achieved so much popularity that Valve hired the developers and marketed the product as a stand-alone title. Counter-Strike is a modern day incarnation of cops and robbers. One side plays the terrorists, the other side plays as counter-terrorists. The game has been played competitively at the highest levels of gaming tournaments. It continues to get patches, updates, and fixes, over 10 years after its original release. Few games can make that claim. This iteration, Counter-Strike Source is an update of the original game that instead of using the original Half-Life engine, uses the Half-Life 2 engine. The changes are mostly cosmetic, offering better graphics, higher resolutions, and more realistic animations and physics. It's the natural evolution of the game with better technology behind it. In order to get Counter-Strike Source to work, you must first own a game that already uses the Source Engine, such as Half-Life 2, Team Fortress 2, Portal, or Left 4 Dead 1 or 2. Or, you could just purchase it directly.
