Pretty good price for the game considering it's still $40 on Steam after almost 2 years. Not the cheapest ever though but still a decent price that I can find at the moment. And this is a retail DVD (activated on Steam) so it's nice if you don't want to DL a 20GB game off Steam.
Me and my friends mainly play COD just for the multiplayer aspect of it though so fair price for an average game.
Not many people are on multiplayer anymore (basically only team deathmatch and domination) and Ghosts is coming out in 3 months, so you may as well wait.