CoD4's plot is fine - I actually really enjoyed it. It's my favourite CoD and one of my favourite shooters.
MW2 was fun, but too short of a campaign and the plot was less impressive and a bit jumbled. (Will MW3 pull off a No Russian?)
Black Ops had an interesting twist. I kind of saw it coming but everyone seemed so... surprised. Really you guys? You didn't see/hear the many hints?
As for the multiplayer, you gotta enjoy it while you can before the 12 year olds and hackers show up. Open lobbies before their bedtimes are all kinds of...special cesspools.
...I'll probably get MW3. Always preferred Infinity Ward over Treyarch, let's see if that holds up even without West and Zampella. Plus I still want to kill Makarov.
For all of the Activision hate, they do have a hell of a marketing department. I love the Black Ops TV ad and the map pack trailers. Commercials are supposed to make the game look good anyway - I still love the Infamy trailer for MW2.