TG CS:S is much slower than 2142. You know, how in 2142, having artillery, a walker, an APC and a dozen targets on your screen is considered frantic? In CS:S, frantic is 3 players on the screen. You might spend 3-4 minutes sitting in a spot with little action. The game-play is more personal, one shot either way can change the whole course of the round. I've seen teams get decimated because the sniper got taken out early in the round.

2142 is a more strategic team-based game, whereas CS:S has a bigger focus on individuals and midgame tactics. 2142 has a completely different kind of command structure: Commander tells his Squad Leaders where to go, Squad Leaders tell Squad Members who to kill, and Squad Members kill them. In CS:S, you might have a leader, who calls the shots, but a lot of the time you decide as a team what you intend to do. Plans are important, but even more important is adapting to a new situation. Since the whole balance can shift thanks to a single shot, plans have a tendency to change. Some of my most "successful" plans have gone from "pick at A" to "Rush into B."

Maps are more CQC- orientated. Most are filled with chokepoints, are generally more "unique." The game is played on a much smaller scale, so small details, like boxes, doors, windows and sometimes even plants and paintings will play a bigger role in game. Another big difference is that most maps have highly used hiding spots, so knowing the map will be as usefull as being a good shot. I'm not saying you'll immediately know where everyone is hiding, but you'll know that the enemy might be up in a certain window, or on top of a certain beam.

Overall, the 2142 is a strategic game, with a bigger emphasis on the overall game, and in CS:S tactics play the important role.