CoD1 on Steam: 1 minute.
Played it way more though because that game existed long before Steam.
CoD2: 8 hours
CoD3: 0 hours
Console only?
CoD4: 26 hours
CoD5: 5 hours of the beta. Never played the full game. (I denied to buy it because IMO it was a $20 expansion pack to CoD4)
(EDIT: I just remember I DID play ~2 hours of Nazi Zombies on XBox in this game. But it being on XBox I don't think I can call that "playing". More like being frustrated about the lack of proper controls)
CoD6: 3 hours singleplayer (till end)
21 hours of MP
CoD7: 20 minutes of SP
~20 hours of MP of which at least 15 had to do with development/game was minimized.
CoD8: Never started SP
~10 hours hacking on MP; then got bored (last started 2 months ago)
Team Fortress 2: 1800 hours
Counter-Strike Source: 750 hours
UMAD ACTIVISION?