Here is why I like CoD.
1) It is fast paced.
2) Allows for people to put together a clan in relative ease.
3) Doesn't require an expensive computer to run.
4) Fairly balanced PvP (Black Ops is claiming to be the most balanced CoD yet, but we'll see)
5) Anyone speaking trash into the mike, you have a chance to make him regret those words.
Honestly, without a dedicated computer to run superb FPSs, CoD is the Average Man's FPS so to speak. Each iteration actually brings more fun in my mind. Half the battle is learning the ropes. After getting enough skill to be average, it get's a whole lot more fun. People also hate on it because it is popular. You don't see me running around calling CS trash? I have actually played it, I am just not on a great computer, and have a lot less skill because of a physical disability. This means I cannot play on M & KB effectively because when I get adrenaline pumping, I start to twitch, and in the process hitting other buttons unintended, and hitting buttons too fast. No, the main reason its hated on is because it is popular.