Only time will tell which is better.I voted for cod4,as I have been there since day 1,but halo 3 ,in my opinion,has slighltly better online play.
I do prefer my game play to be more realistic,and cod4 is in a class of it's own with it's graphics.Could this be more realistic?Some of the visuals are outstanding-especially "all ghillied up".

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"Police up your spare rounds and frags.Don't leave nothin' for the dinks." Sgt Elias Grodin-Platoon