I'd personally say COD4 is better in campaign and online. The campaign actually has a storyline whereas halo cortana somehow gets kidnapped and you run around blowing up covenant. COD4 has a purpose, to stop the russians/Iraqis and stop a nuclear war. The online I think is better too because I like realistic games better, I'm not into the 1 whole clip=1 kill type games with a rifle. I'm into 2-3 shots with even a pistol=a kill but that's just me. No one can really say which ones better though because it all matters about opinion. Ask a 5 year old they'd say Hello Kitty is better, that's their matter of opinion.