Here is my take on the CoD series.
My first one was CoD Finest Hour on the gamecube. I remember none of it.
Moving on; next one I played was CoD2. Pretty decent. Was one of my first 360 games, and CoD2 and PDZ were my main multiplayer games at 360's launch.
CoD3: got it for Christmas, did not like it at all.
CoD4: My favorite console shooter ever. This game really revolutionized modern shooters, whether you like it or not this game has influenced all kinds of games' multiplayer modes. Also introduced me to my favorite gametype ever: Search & Destroy.
CoD WaW: Did not like. Clone of 4 with WWII skins, horrible animations, muddier textures made for worse graphics, no one wanted to go back to WWII after the ridiculous amounts of WWII games back then. I also do not like Treyarch, I feel like they're riding IW's coattails. Although I do applaud them for the great zombie mode, which was the best part of WaW.
CoD MW2: A horrible mess. The multiplayer was so unbalanced and full of glitches. Remember those akimbo shotguns that you could snipe with? The javelin glitch? Infinite care package glitch? One man army + danger close noob tube spammers? Quickscoping aided by sleight of hand pro and the atrocious (as in it basically aimed for you) auto-aim? Commando + marathon + lightweight + tac knife? The only good thing about this game was its better graphics. If you can see past the HUGE imbalances it's decent though.
CoD BO: I don't understand how a sequel actually has worse graphics than its predecessor. This game is ugly, maybe they cut back on graphics for the 3D support, I don't know. Other than that I enjoy the game, decent SP, loved the wager matches, and MP is way more balanced than MW2.
Overall: Ever since CoD4 the CoD series has been worse than it should be. By that I mean look at the difference between CoD2 and CoD4. There were big changes, and now that Activi$ion is getting money they're intentionally taking smaller steps to milk as much as they can.
The CoD series is good. It doesn't matter if you hate CoD, but your hate doesn't mean it's a bad game. Compare CoD to other shooters like the mediocre title "Timeshift." CoD has polish, runs smooth and has decent gameplay. Being a hipster and hating the mainstream and popular game doesn't make you cool or hardcore, infact I consider myself a hardcore gamer and I enjoy CoD.
TL;DR: CoD is popular for a reason, and Activi$ion is the problem as far as I'm concerned.
EDIT: And yeah I lol'd at the "pumping out new content, no game is ever the same." Don't lie to yourself, they've stopped innovating and are just adding tuny features to each title and calling it "different." Every CoD after 4 has had the same exact core gameplay.