NO! I did and it was a HUGE mistake. You don't need a CD key, but this thing is fucking horrible off there... waste of $45 (bought it on sale)...
Problems I have (I might just be unlucky though):
- Can't find any coop servers...
- Can find regular servers, but always have trouble connecting to them...
- Can't change resolution or game minimizes and never comes back up...
- Updates we get about a week or two after everyone else (meaning people who bought retail PC version)
- No real support from either Steam or Activision on... messaged both about issues and nothing...
- Heard a rumor that mods don't work, I never tried it since I couldn't get multiplayer to work anyway...
As for how it runs, basically you just buy it off there and it gives you one launch icon... half the time it asks you if you want to launch single player or multiplayer when you click it, other times it just starts one and you can switch to the other on the menu screen... If you are going to buy it, take the safe path and buy retail...