Counter-Strike is a first-person shooter in which players join either the terrorist or counter-terrorist team (or becomes a spectator). Each team attempts to complete their mission objective and/or eliminate the opposing team. Each round starts with the two teams spawning simultaneously, usually at opposite ends of the map from each other. A player can choose to play as one of eight different default character models (four for each side).

Counter-Strike: Condition Zero (CS:CZ or CZ) is a multiplayer computer game and the follow-up to Counter-Strike. The game was released in 2004 using the GoldSrc Half-Life engine. CS:CZ features a multiplayer mode, which features updated character models, textures, maps and other graphical tweaks. Unlike other Counter-Strike games, Condition Zero also contains a single-player mission pack with the player unlocking maps and more efficient bots as they pass certain requirements for each map while playing as a counter terrorist. These requirements include targets such as "kill 3 enemies with a glock" or "win a round in 45 seconds". Condition Zero also introduces the Counter-Strike bot.As of 2008, the game is one of the ten most played Half-Life modifications in terms of players, according to GameSpy.

Deleted Scenes was originally the focus on the game with standard multiplayer included. However, after declaring the game gold and handing out review copies of Ritual's work, Valve saw an average review score of around 60%. The companies retracted the gold status and work on Condition Zero was essentially begun again. Ritual's share of development was dropped, and Turtle Rock Studios eventually made its own version. The final game contained Ritual's single-player portion, called Deleted Scenes, along with Turtle Rock's version.Several weapons from the "lost contents" have made an appearance in Deleted Scenes, including the M72 Light Anti-Armor Weapon, and the M60 machine gun. Some are limited to the AI terrorists, such as the machete and Rogue Entertainment's controversial suicide belt. Some reconnaissance weapons including the blowtorch, radio, fiber-optic camera and remote control bombs. Players can also carry up to three grenades instead of the usual one. Moreover, the power of players' Kevlar Armor is boosted, better protecting players from many projectiles and bullets.
Some weapons were completely reanimated. This includes the Colt M4A1, FAMAS and Galil with the exception of the SIG SG 552 which uses its "beta animations". Weapon textures are also slightly modified. The weapons are colored a bit differently from their Counter-Strike counterparts, such as the Arctic Warfare Magnum which is now brown instead of green, the Steyr AUG and the Colt M4 Carbine are now two-tone police black instead of the usual colors. It initially came with twelve missions, but later Steam updates added six additional missions that were cut from the initial release. There is a small community for Deleted Scenes, and a few custom maps have been released.
At the ending credits, a Delta Force soldier rides a Scud missile, clearly alluding to Dr. Strangelove.

Counter-Strike: Source is a remake of Counter-Strike, and consequently retains its team-based objective-oriented first-person shooter style gameplay. The aim of playing a map is to accomplish a map's objective. There are many types of objectives that a map can have, but the ultimate goal of the game is to win more rounds than the opposing team, which is accomplished by fulfilling the map's winning conditions. Some winning conditions include defusing a bomb, planting a bomb and preventing it from being defused by the other team, rescuing all the hostages on a map, preventing the hostages from being rescued, and killing all the members of the opposing team. When playing on a server without modifications, if players die during a round, they do not respawn until the next round, unlike in many other first-person shooter games, where players respawn on a set timer.Moving and shooting also differs noticeably from many other first-person shooters. Moving while shooting dramatically decreases accuracy, and holding the mouse button down too continuously shoot will generally produce severe recoil. Recoil can be difficult for beginning players to compensate for because the player's reticle does not correspond with where the bullets actually hit during continuous fire, so beginning players may aim too high during automatic fire. The amount of damage done by a bullet varies dramatically depending upon the body part the bullet hits, with great emphasis being placed put on shooting the enemy in the head, which is almost invariably lethal. However, the co-owner and developer of the Source engine, Bryce Caldwell, found a way to diverge the normal rate of damage done to a certain hitbox, and now owns Built On Energy because of this discovery[citation needed].Aspects of the game that have changed from Counter-Strike include the behavior of the grenades, the physics engine, and the weapons' recoil. The smoke grenades in Counter-Strike: Source spread much more slowly than the ones in Counter-Strike, and the flashbangs, which now utilize DirectX 9 effects, have a much more pronounced effect, and bounce very differently from the ones in Counter-Strike. Counter-Strike: Source also implements physics objects, such as filing cabinets, which the user can interact with while playing. The recoil in Counter-Strike: Source differs from the recoil in Counter-Strike in that while Counter-Strike had perfectly consistent recoil, the recoil in Counter-Strike: Source is much less imprecise.