The multiplayer in Call of Duty is casual at its core.
The main gameplay has some depth, but it is designed around "keeping the field together" ...
It is very easy to ge into, you get rewarded for playing poorly and even for dying. Mix in a MMO-like progression to motivate the players and you have the ultimate casual shooter. It's essentially the shooter version of Mario Kart. The killstreaks are the blue sheel. This is not something bad, It definitely does it's job well for being an entertaining shooter with solid mechanics. It just shouldn't be compared to something like Counter Strike, Quake or even Battlefield.
The single player is the gaming equivalent of a Michael Bay movie. Not necessarily bad, but not designed to be anything other than a roller coaster ride. Playing the single player a second time will make it crack.
Now hate is strong word, I don't hate the game and they are usually decent products with a decent amount of content. On the other side I can't help myself to feel like the people who buy it each and every year are huge suckers.