first person shooters in general are all very similar therefore the gameplay is similar through most of them style games. I guess you are a fan of COD so you will fail to see how shoddy the games are. The only good thing I have ever seen to them is the multiplayer aspects as singleplayer was always atrocious in COD
You can't really drive an argument with the point that its an FPS. Just because there's a lot of them doesn't make it a bad game. You can apply that to absolutely any genre.
Your second point... On what grounds are they shoddy games? I can tell you, there are FAR worse games around.
And your point on the singleplayer... CoD4. And the others are by no means bad. They aren't spectacular, but you can't use them to drive an argument bashing on the franchise.
You want a bad singleplayer? MoH Warfighter. Absolutely sodding awful.
I know what you'll say next, 'I'm not going to argue because you're a fanboy and I wont be able to convince you otherwise' or something along those lines. I'm not a fanboy, I simply don't understand the logic of those who hate them simply because of the name.