CS struck a great balance between skill floor and skill ceiling, which is one of the reasons I think it was the first blockbuster multiplayer FPS: even if your opponent is a way better player and knows the map, it's still possible to get lucky and win. The same isn't true of games with a higher skill floor like Quake duels*

*RA3, a Quake mod which came out around the same time as CS, lowered the skill floor by giving players a full loadout of weapons and maximum health on spawn. It was good!