What do you think of Call of Duty 4? Do you play it online? If so what is your weapon set up? Personally I think it is the best COD of the series and VERY addictive!
I play the game quite a lot and really enjoy it, so much so that I made a strategy site for it. There is a link in my sig if you are interested.
I love it I use either the M4 carbine or MP5, depending on what level and what mood i'm in. Also have the desert eagle on standby incase any close encounters happen (faster to switch than to reload).