It's true that the games inside the same series in the Franchise are similar, but is it really different from any actual franchise? Can we say that Pokémon games are different from each others, or Kirby games, etc?
Not really.
Yeah, but you're biased ;p
And also actually correct. Any franchise that runs for awhile without completely reinventing itself from the ground up begins to get familiar, but whether that's a bad thing or not is up to the player. Pokemon is basically the same game with new creatures and a few new features. Mario platformers are the same game with new levels and a few new power-ups (barring the reinvention into 3D, which... oh look, it reinvented itself).
CoD is a fast-paced, fast-death shooter series with a focus on multiplayer. That's true of pretty much all of them from Modern Warfare on - which was the point the series reinvented itself. But
within that space it's always attempted new and interesting things, some of which worked, and some of which didn't. BlOps 2 did some really clever stuff and
still got a lot of hate for being the same thing again, because it's still a fast-paced, fast-death shooter game with a focus on multiplayer.
There's an argument that CoD could probably do with taking a year or two off, but with multiple teams working on multiple iterations at once and with sales still peaking pretty goddamn high, why would they?
It's not so much that the franchise is failing; it's more that tribal mentality has led to people falling into the camps of the people who play it and the people who don't, and the longer the series runs with annual releases, the louder each camp gets.