Here's a brief summary of what CS:S is really all about.
Counter-Strike: Source (also known as CS: Source or simply CS:S) is a multiplayer, team-based tactical first-person shooter, developed by Valve and Turtle Rock Studios. It is a remake of Counter-Strike, the 1999 modification of Half-Life. Built on the Source engine, the game was released in 2004 along with Half-Life 2.
Similar to the original version, Counter-Strike: Source games involve a team of counter-terrorists facing off against a team of terrorists in a series of rounds. Each round is won by either completing a mission (such as detonating a bomb or rescuing hostages) or by eliminating all members of the opposing team.
Counter-Strike: Source gameplay differs to other multiplayer first person shooters (often called "deathmatches"). Most prevalently, rather than "respawning" immediately after being killed, Counter-Strike players have only one chance per round, and, if killed, must wait until the next round to continue playing.
Whereas in other games players are able to collect a wide arsenal of weapons (such as in the Unreal Tournament series of games), CS:S players must purchase a specific set of equipment and weapons at the start of each round. Each team spawns in a "buy zone", which is the only area of the map where items and weapons can be purchased. A small amount of money is allocated to each player at the start of the game, and further funds can be accrued by completing certain tasks during the round (such as killing an enemy or being on the team who wins the round). This is totaled at the end of each round, and available at the start of the following round. Players can also lose money by killing teammates or hostages.
Furthermore, there are limits imposed as to how many items a player can hold at once. Each player may hold at most one main weapon and one sidearm, plus a small number of grenades and other equipment (such as defusal kits, body armor, or night vision goggles). Also, no player may accrue more than $16000.
Counter-Strike: Source features the same weapons as Counter-Strike:
Pistols: USP, Glock, Desert Eagle, P228, dual Beretta .40s, and the FN 5-7.
Shotguns: Benelli M3 Super 90, and XM1014.
Sub-Machine Guns: MP5 navy, Steyr TMP, P90, MAC-10, and the UMP.
Rifles: Galil, FAMAS, AK-47, SG-552, M4A1, Steyr AUG, Scout, AWP, G3-SG1, and the SG-550.
Machine Gun: Minimi Para
CS: Source is more of a tactical-shooter than deathmatch-style games, such as the Quake and Unreal Tournament series, but it does not put as much emphasis on tactics as other titles such as the Rainbow Six series. Players can devise their own strategies, either through the radio communication, in-game talk, or through external programs such as Teamspeak or Ventrilo, which are often used in clan matches.
Purchasable equipment such as flashbang and smoke grenades can be used to create cover or distract the enemy, and the teams can split into smaller squads and take different routes through the maps.