The Ultimate competition for online gaming. Great graphics, value, and combat as realistic as you would want it to be.
The game itself is simple...elimanate the entire other team of players or complete the objective (disarm bomb or resque hostages) Thats it. Buy a wide variety of guns to make any of those things easier. The graphics are of course over the top, because of the game running off HL2's powerful engine. Dynamic lighting, sounds and physics make this one of the most realistic shooters to approach the gaming world ever.
As any CS player would know, Source takes reflexes, teamwork, and concentration. Obioulsy being an online game, there are hundreds of people that can do none of the above. So by having a crappy team and losing repatively makes for some lously games. The best "checks and balances" that this game has is AI that evens out the numbers of players on the teams.
But like other modern games go, there is an Administration system that lets certain players control. Almost a whole world in itself, one could play CS for hundreds of hours in diffirent levels, using diffirent guns, with diffirent mods present.
Buying the Half-Life 2 package even includes the SDK or Hammer and mod editor that lets the player create their own levels for online play, or make single player levels in Half Life. Bots for both CS and HL are included and have fast and effective tactics, but sometimes get stuck of top of chairs or jumping continusly into a wall.
After hundreds of house spent playing CS:Soruce, I think I can say that people who are good at the game will love it and people who suck at it ( "Noobs" ) will most likely despise it.