Pokemon games are like COD games, same thing with more bells and whistle, however they are still a lot of fun. Many people are entertained by the same old thing as that thing is very very entertaining. People do not need something brand new and totally different to stay tuned. Of course people eventually get bored.
There is a big disconnect from hardcore gamers that exist on this site compared to reality. Online Black Ops is the worst game, in the real world, people love the mutliplayer like crazy.
I was with my friends and asked how they liked Black Ops and they said it was great and have all per-ordered MW3 (many were pre ordering first time.
They all heard about Battlefield but appear to be focused on MW3 first. So I think Battlefield will have good legs.
So, all I am saying is COD is series that appeals to the masses and is very successful. You can look at any form of entertainment where this has happened and people start to hate on it (game, movie, book, etc), due to its success.