We talking about the whole series here? B/C I never liked COD til Modern Warfare I and while that was a GREAT game for me, I haven't really played any of them since. But Halo 1, 2, 3? Those were the crackiest of crack during college times. Last shooter I played offline and first I played online. Last shooters I enjoyed the campaign in too. I could pick up a COD and enjoy multiplayer after a lengthy reflex tuneup, but I wouldn't have the least interest in campaign mode or whatever you call it. And I'd be just as or more likely to grab a Battlefield. That said, I'd probably be more likely to get a Resistance or something than jump on a new Halo. Maybe I'd give Halo IV a shot.
Halo > COD
P.S. it's not supposed to be realistic. They are space marines. Fighting aliens. In SPAAAACE!
This was the world that I had created. I know what I have to do to fix it...to make things right. There's no problem that can't be solved.