i´ve been hearing that serie is in decline but know i saw that this is the best selling Cod ever on Xbox...

So what am i missing?

The series is not on decline.

Black Ops 2 will top MW3 this year.

Its not on a decline, just ignore analysts. They try to detect the decline in everything, even when its not there.

Black ops 2 looks to be trying a lot of new things for the series, + Zombies so im thinking Black ops 2 will top MW3 easy.

No decline yet. Not sure where that statement came from.

From misinformed analysts like Pachter.

They were cherry picking a small period where MW3 sold less compared to Black ops.

Its not true. Next question.

As far as the series become more and more known it's expected for it to be more and more front-loaded.

Unfortunately, dumb annalists will see this difference as a decline while smart people will see it as an increase on the series popularity.

Even if it is on decline - which is not the case - the sales are absolutely amazing to last a couple of entries more before the series reach low sales.