Not to go against the grain of the thread (<- lies) but I really cannot stand CSS.
Why? It's too bloody frustrating. players basically come in three varieties: the complete n00bs who think it works like any other deathmatch, the good players and the godlike players.
I'd place myself as being average-good. I can reliably score a headshot with most of the weapons in the game.
The frustration arises from the fact that death, in CSS, is BORING. You spend the rest of the round, however long that lasts, watching other people play.
the other frustration is that, regardless of how many rounds there are in a game, it's damn near impossible for a team that suffers defeat in the first round to win thereafter, as they have to spend funds on re-equipping, while the winning side starts to rack up a collosal amount of money- more than enough to re-equip team members who fell in the previous round. After two or three rounds, you wind up in the situation where one side is wielding nothing but pistols, and the other side is packing helmeted kevlar, two or three types of grenade apiece, plenty of spare ammo, and a good gun. in such situations, it really does become almost impossible for even the most skilled teams to turn the tide.
My final gripe is that the elite few players (there's one here at my university called "fak3") can single-handedly take on an entire opposing team and win. the guy I just mentioned can score headshots using a decent pair of stereo headphones - he hears where the incoming enemy soldier is, judges where they'll be in three seconds, judges where their head will be at that point, aims there and... splat. One shot. Headshot. through a door. without ever seeing the target.
I played it for a while, and just realised that it's not as much fun as it first appears.
I prefer "Dystopia" myself.