Objectives and Teamwork
Objectives are a big part of Counter-Strike, and teamwork is the most effective way to achieve those objectives, so the Rambo-like solo wrecklessness of many earlier shooters is a lot less common. Earlier mods had objectives, but none were quite as well-suited to the theme as the ones in CS, where you weren't capturing some esoteric flag, but planting bombs and rescuing hostages. Few games can equal the excitement of a CS match that comes down to the last Counter-Terrorist defusing the bomb with only seconds to spare.
It could be argued that every multiplayer FPS since Team Fortress has involved some sort of teamwork. The difference is that teamwork is central to CS, rather than being a rarely realized possibility. Part of the reason for this is that you spawn with the rest of your team - selecting some spawn point on the other side of the map is not an option. The nature of the objectives and the layout of the maps contribute to the need for teamwork, and in practice, the more organized team almost always comes out ahead.
Balance
Having just turned five years old, Counter-Strike has had a lot of time to mature, all of it filled with robust community feedback. By the time version 1.5 was released in June of 2002, CS was not only extremely refined, but boasted several features, such as radio commands and voice communication, which we are only beginning to see in current games.
While certain weapons, such as the Arctic Warfare Magnum, will likely always be a matter of contention among CS players, balancing a few different types of guns is inherently easier than balancing tanks, planes, and ships right along with foot soldiers. In fact, if a guy in a plane doesn't have an advantage over the average rifleman, realism suffers. It may be a product of the more limited PC technology of half a decade ago, but the simplicity of the terrorist theme in CS was a natural fit for a first-person shooter. The latest games which feature vehicles and all sorts of advanced weaponry can make it comparatively difficult to get into a fair fight.
Maps
Fortunately, some good map makers got behind CS and made some nicely balanced maps for the game early in its development, particularly for bomb/defuse scenarios. Maps like de_aztec, de_dust, and de_nuke are well-suited to this type of contest, which wouldn't work on maps that are too large or have too many hiding places. By the time the retail version of Half-Life: Counter-Strike was released, it included a healthy variety of maps for the game that kept the action close at hand.
Technology, or Lack Thereof
We can safely assume that there are quite a few CS players that simply don't have a PC capable of running newer games. If the Steam hardware survey is any indication, however, the vast majority of people are playing on a system that greatly exceeds the game's requirements. It's evident that they either want incredible framerates or something is keeping them in the game besides the limitations of their hardware. I think it goes to show that graphics can only take a game so far - what keeps people coming back is solid gameplay.
Pace
Sometimes it is the more subtle elements of a game, be it the atmosphere, the lighting, the sound, or just the overall feel of it, that take the experience to another level. Returning to CS after a lengthy hiatus, I couldn't help admiring the pace of this beloved mod. Within seconds of spawning, you're in a vicious firefight with the enemy. Every corner you creep around is a potential death trap. Every kill brings with it the satisfaction of knowing that there is one less player between you and your objective. Even sitting out the remaining few minutes in a round after dying is not without rewards, as it gives players a chance to socialize and speculate on what went wrong. It may not be perfect, but it remains one of the most suitably proportioned shooters available.
Given that Counter-Strike has long been the impetus behind Half-Life sales, and has extended its reach to the Xbox, I wasn't too surprized to hear that Half-Life 2 will include an adaptation of CS to the new engine. It will be interesting to see if the remake of this classic shooter can win the same kind of dedication from the game community as its predecessor.
