i've been playing CS:S like mad lately. if you find a good server with decent people to play with, it's a great game. i normally play on only one server (24/7 Office Server) since the same people play there everyday. if you join any one of the other less-than-satisfactory servers, your gaming experience will suck.
i tend to stay away from the extra large capacity (40+ players) servers due to speedhackers, wallhackers, aimbotters, etc., but still run into them on occasion with the better servers. when VAC (Valve Anti-Cheat) is finally released, hopefully the user experience will be even better.