Most weapons have increased first-shot accuracy thus burst-firing can be more effective than in older games. This is further strengthen if the dot in the middle of the crosshair is enabled.
The AWP and Scout have quick scope accuracy penalties, rendering "quick scopes" ineffective than in previous games.
Holding down the firing button has the same effect. Moreover, the player can only fire two rounds when holding down the firing button and the third round will not fire until the player releases the fire button and then presses it again.
The AWP and Scout have longer reload times. Both rifles now feature the user cocking the rifle after the insertion of the magazine.
The "quick attach or detach" trick of silencers has been removed; you now need to fully play the attach or detach animation. It will reset if another weapon is drawn during this process.
Maps have been modified, some to a greater extent than others. For example, on the map cs_assault, the highway straight across from the Counter-Terrorist spawn zone was changed into a railroad station that needed stairs to climb up.
The scale of the players relative to the map has increased slightly. However, movement speed remains the same.
Bullet wall penetration is massively reduced.
Low caliber rounds can now penetrate through unbreakable glass and thin walls. This eliminates glass material as a shield and damage will be reduced.
Hostages will not become stuck in one place anymore unlike in CS 1.6, where some areas can cause hostages to become stuck permanently until the next round.
Some doors now require to press the "USE" key to open.
The Source engine allows more sophisticated physics, such as "interactive" props on maps (e.g. barrels). Shooting these props will cause them to move around the environment.
Moving physic props can kill players if there is sufficient momentum. This is usually seen when barrels are launched by the explosion of a C4 and are launched at the direction where a player is. (A victim will get a -1 point in the scoreboard but it does not count as a death.)
However, unlike the physics engine of Half-Life 2, a player will bounce off when he collides with a prop rather than colliding it and having reduced movement. (For example, a player can jump onto a table but will fall off as soon as he jumps on it.)
Throwing grenades into a sloped area will cause it to roll.
Flashbangs and receiving damage from HE grenades now affect hearing. Flashbangs also affect vision by a different amount of time. Also, when blinded, the bleeping sounds that are heard are reused from Half-Life 2 when a player is damaged by explosive weapons. All players' status (HUD) will disappear until they recover from a flashbang.
HE grenades no longer deal damage through walls, However to compensate this, these grenades deal more damage to armored opponents.
Moreover, just like the flashbang, when the player takes explosion damage, the player will hear a bleep sound.
Smoke grenades give off much more smoke and causes more obstruction of view. Also, unlike in 1.6 where names of players will still appear when pointed at him, the names won't appear if they are within the smoke.
Thrown grenades, flashbangs, or smoke grenades no longer open doors when it hits them.
Moreover, the collision boxes have the same size as the model whereas in Counter-Strike, they were smaller than the model.
Grenades can deal 1 point of damage when thrown directly at a player and it will also slow his movement for 3 seconds.
Player models no longer flinch when taking damage.
Players will aim firearms on the shoulder instead of the hip in third person, with the exception of the AK-47 (as Terrorists) and the M249. However, if the player is moving, they will hold firearms on the hip.
All weapon reload sounds now uses proper sounds in third person instead of using the AK-47 sounds.
When reloading, the magazine will properly appear unlike in previous games.
The attached silencer will be seen in third person. Also, removing it will take out the silencer in the third person view. However, there are no animations in third-person.
Most weapon animations in third person uses now the proper animation. For example, if a player fires the AWP, the AWP in third person can be seen operating the bolt after each shot instead of an empty shell being ejected from the rifle. The reload animation has changed as well; some weapons now have unique reload animations rather than sharing the same weapon's animation.
For shotguns, instead of simply inserting one shell in a shotgun in third person, it correctly shows the player individually inserting the shells into the shotgun.
For grenades, there is a third person animation when pulling the pin of grenade off.
When shot, blood will appear on the player's skin, much like the NPCs from Half-Life 2.
When the player takes damage from headshots, large blood sprites will not appear. Instead, normal blood splatter sprites will appear.
Upon dying, the bodies of players will turn into ragdolls upon death instead of using the usual death animation(s), this is very apparent if the player is killed by explosives. Moreover, the body can be moved.
The mouth of a player model no longer moves when using a microphone.
All weapons carried by the player is shown in third person.
Pressing the "USE" key through a wall is no longer possible.
Players can now perform "USE" key actions while reloading. In older games, it can only be done with shotguns.
When killed by a headshot, players will not make dying sounds. Only the impact sound is heard.
If the player died because jumping the high area while having low health, the bone-crunching sound will not be heard when the player died.
If the player died by grenade or the method above, the player may hear a Headshot sound when dying.
When the last hostage is rescued, the announcement will say "Counter-Terrorists win" instead of "Hostages have been rescued" whereas in 1.6 and Condition Zero, this announcement is only heard when at least two hostages are rescued and the other hostages are killed.
When the C4 is defused, an announcement will say "Bomb has been defused" rather than "Counter-Terrorists win". Prior to CS:S, this quote was only heard in the training map of CS 1.0.
The map features of the Source interface are more informative. For example, on the radar, when a teammate or an enemy player is killed, an X is displayed corresponding to where the teammate or an enemy player has died. Map overviews are now shown on the radar.
Radar now shows enemies spotted by you or your teammates.
Radar/map overview is shown whilst spectating.
Radar when spectating shows line trails when players move around.
When the C4 is dropped, any CT members that are in the view of the C4 will appear on the radar (only when the C4 is pointed close to the crosshair).
Although the ammunition options have been removed from the buy menu, it can still be purchased (for free) if a player returns to a buy zone (assuming the buy time hasn't expired) using appropriate developer console commands (default = , [comma] and . [dot]). When the next round starts, your weapon will be given full ammunition and you don't have to purchase it. (You have to survive the previous round though). It is also possible to select the option "re-buy previous weapons" to gain full ammo.