COD4 is a very good game. I (like terghazi) tend to play Hard Core Search and Destroy. However, if you play online (especially a console) be prepared for a lot of harassment from young boys who have not hit puberty yet. The smack talk is less fun and more a lot of f-bombs and homo-this and ... well you get the picture.
Having said that, the single player game was fun, but the online mutliplayer is the real reason to play. Especially building up the achievements.

"What can be asserted without evidence can also be dismissed without evidence." C Hitchens