Meh it changes enough to keep things interested. Plus Infinity Ward games don't play at all similar to Treyarch games even though its the same core gameplay mechanics. So its only "the same" game every other year.
Its not like Battlefield revolutionizes every installment. Bad Company 2 was a carbon copy to Bad Company 1. And while Battlefield 3 is on a new engine the gameplay looks the exact same to a non-fan of the series.
I do agree CoD is in need of another major overhaul (like CoD4 was compared to CoD3) but I don't think this series deserves all the flak it gets.
The problem isn't the game (for the most part) its the community of 12 year old whiners and people who exploit overpowered guns, killstreaks and perk combinations. Besides not adding dedicated servers (no idea why besides greed/laziness) they are doing all they can to make the series better.
