The History of Why I’m Tired of Your Modern Shooters (2011)

To put it bluntly, one of the main rules and joys of CS is to shoot people in the head. All else being equal in a firefight, if you are good enough to get a head shot and the other guy can't, you win every time. Part of this is strategy (money/weapon management), tactics (positioning, maneuvering, footstep sounds) and aiming/reaction speed/firefight maneuvering. The main difference in CS:S affects the last category. CS:S added more randomness, changed recoil, changed the spread of bullets and hit boxes. CS:S de-emphasized the head shot, presumably to make the game less challenging to beginners. They changed the physics of grenades, running, jumping making the whole thing feel more sluggish.

Then there is the presentation part of it. CS made it very clear when you hit a head shot versus a body shot. For example, a head shot when the other player had no helmet resulted in a big spray of blood. When having a helmet there was a big spark shooting off of the head identifiable from afar, and also a satisfying sound. There was also a very different death animation after a head shot versus a body shot. A head shot would result in the player violently falling backwards, while in CS:S the player would just slouch to the ground like he tripped on a stone.

CS:S also added a lot of visual clutter that is nothing but detrimental to gameplay. Adding clutter to a competitive game hides the true important "signals" in the game, head shots being one, and just adds noise. This is why pros tend to strip down a game to the bare essentials if they can (look at Q3 for examples of this).

Another factor that adds to the "feel" is the weapon models and sounds. This is subjective, but the sounds in CS feel more powerful to me. Compare the important weapons like the ak47, the colt, deagle and AWP.

These are the reasons that "pros" never switched to CS:S, or if they did (usually because of prize money), they promptly switched back. Every issue might seem small, but they add up to a worse experience.

Ever since Valve took over CS, they have been going in the direction of making the game easier (giving beginners a chance). They started down this path with CS 1.4-1.6, but much more so with CS:S and now CS:GO. The truth is that if a beginner starts playing CS 1.6 today, he will most likely rage quit way before reaching any level of competency at the game. This is not good for Valve because it discourages new players. But this is the way it has to be if pros will want to stick to the game. There HAS to be a huge difference between a beginner and a pro, otherwise there's just no point in having a competitive game. The other part is also that there is no money to be had in a great 14 year old game that doesn't need much improvement. What CS needs is a better match-making system so that beginners won't rage quit, not changes to the feel of the game or more useless weapons or better graphics.