You mean besides the entire design of the multiplayer, right? Static environments, killstreaks, perks, etc?
Same game, new maps, reskinned weapons. Just because you don't see/feel the similarities doesn't mean they don't exist. Your disagreement doesn't inherently invalidate others' opinions. If this year's expansion pack keeps your juices flowin', then more power to you.
"Good" is a very relative and personal term and its definition is up for huge debate. If by "good" you mean "lots of sales," then yes, CoD is good. By that definition, Madden is also "good." The definition *I* use for good is a game that pulls me in and keeps me coming back. CoD is having a very difficult time doing that for me these days because the game feels so damn repetitive. My subconscious sees it as a polished/tuned version of last year's game. If that's good enough for you, fine, but recognize we don't all have to share your view.
Tiny bumps in graphical fidelity combined with a few new perks, killstreaks, and new maps isn't going to cut it forever. How much patience each of us has for that is different. CoD 4's brand of shooter was still new enough to me that I got off regularly on MW2 and, to a lesser degree, Black Ops. My time is up, though, and that's all I'm saying. Others got their fill with CoD4 and don't see enough if the other titles to keep playing it.
Whether you like it or not, the longer Activision keeps this cycle of rehashing up, the more and more people there will be disagreeing with you. There's a reason there's so much more hype right now for BF3 than there is for MW3. We could have a never ending debate on that if we wanted to, and I don't, but it's going to be tough to bury your head in the sand when the two go head to head this fall.
At any rate, I think your issue is you don't recognize that the basis of this entire argument is purely subjective, but you pass your claims and opinions off as if they're somehow grounded in irrefutable fact. They're not.