The thing is, the thing that makes CS continue to be played while all the other games come and go -for example I'd been playing CS a long time when CoD1 came out, and Im still playing it now when CoD4 is around, and no doubt when CoD8 is out CS will still be played, and still be more popular- is that it rewards you when you win, by giving you more money.
Every other FPS game I can think of is spawn run about die spawn run about die ad infinitum. One of the main tricks to playing CS is Stay Alive!
This can take some getting used if you normally play TDM games, I know when I went from Quake 2 to CS it took me ages.