OK, reading all this and listening to the people I party up with I think I'd like to lay the following out for consideration (and this is not aimed at anyone at all, not matter what you think)....
You don't like Carenten? Don't play it.
People won't die in core? Try hardcore
Got a guy holding down a street with an AR (legit tactic as opposed to camping in a corner)? Choose another route
Shotties are overpowered? Change you style and try to use one
Certain maps (or all maps) are sniper friendly? Try using a sniper rifle yourself
Getting crappy connections/lag? It's CoD, you knew it would be like that when you bought it
Trash talking 8 year olds in the lobby? Start your own party chat, turn CoD music off, put Spotify or similar on and play to your own music
Don't like microtransactions? Vote with your wallet and keep your money in your pocket
Game getting frustrating? Find another game/play private matches with your mates
Getting major rage about it? Keep venting on here and find another game
Remember, that all the tactics, weapons , classes that you feel are overpowered/unfair, etc are open for you to use as well. The only thing you can't do anything about, and which can be a major ballache, is connection
Just my £0.02