It went from a superb and innovative series to a subpar and mediocre one.
I don't hate on people that buy the games though. It's a popular series, I'll give it that. I have met people who think CoD is the best video game series of all time and to that, I just silently shake my head.
And just because I think the series has become stale doesn't mean I can't have fun with it. I think the games are worth $20 at most.