I would call COD4's gameplay to be a little more arcade like than anything. However, what it does have that makes it an awesome game is the combination of everything happening around you to make it feel very immersive.
What makes Call of Duty 2 and 4 (haven't played the first one yet) so awesome is how Infinity Ward has married lots of action on the ground and in the air and also put in lots of great sound effects to make what's going on feel like a larger battlefield than the linear path you'll otherwise be treading. I think this is something that the developers of Killzone 2 have been attempting to try and in some of the footage it really seems to have a Call of Duty inspired feel to them, which I think is great.







