Lets see. The majority of CoD games have no innovation and a 4 hours story. Multiplayer often tries to take away what was good, and replace it with rehash, but leave the bad. It's also usually exactly the same as the last game, just with a few extra guns.
The people who play CoD have a reputation for being tards. Where that it was only a nasty reputation started by rumor mongers, then I'd personally pay it no heed, but unfortunately it's often proven true the moment one logs into any type of multiplayer match.
It's also heavily overrated, and over-hyped. Two things which generally aren't liked by those who have played games for a while. I think I can say that a large percentage of the escapist forum is made up of those whom indulge in nostalgia.
CoD 1 was excellent, but those that followed where just clones of the first one. CoD: Modern Warfare was great to, but once again, all that followed where clones of that other one. So that's 2 innovative, fun games in the CoD series I can count. But not amazing. Which probably causes a lot of hate to be directed their way as lots of people see them as undeserving of their over-hyped and highly rated status.
As for Halo. Its overhyped and overrated, I've also heard to much about it and just want it to stop. Personally however, I hate it because it tore Bungie away from making a sequel to Oni.