Call of Duty campaigns all have what Halo Reach and ODST failed at, unique and awesome action paced goals rather then just running to a base then defending it.
Call of Duty's got the greatest campaign. Compare MW2, which was pretty epic. Then Black Ops, which was like a interactive movie.
Compare to Halo. Yeah, not really. You don't take a break in the middle of combat to show you scoring a headshot in slow mo.