all games are not created equal

The biggest difference between these two games, and ultimately what affects this comparison the most, is what happens once you die.

When I'm playing a game, I want to actually be playing it.  When you die in COD4, you have to wait around for 10 seconds or so, but then you are right back in the game.  In CS:S, when you die, you have to sit there and wait until the next round starts.  Maybe you caught a stray bullet at the beginning of the round.  Too bad, now you gotta wait around a couple minutes until the round is over.

There is a ton more strategy in CS:S than COD4, that's definitely true.  However, for a deathmatcher like myself, COD4 is the better game.