Some would argue it lacks imagination and is stale....just a parade of new maps that cater toward knowing the nonlinear, choke point, hiding spot layout (so buy it fast and study up!)
That each new installment is a high priced map pack forcing you to prestige....but I wouldn't go so far.
They intovate with modes, wager modes, confirmed kills, etc.
I think at its core is that the reality 1st person shooters are more common, somewhat older too on the Online Multiplayer front when based in reality like CoD, BF, MoH, etc.
I dunno. To be honest it bored me away. but that's just me. I was a scary good camper. not squatter btw, there is a difference....
And run and gun on CoD was pointless, due to low health mechanic and how the slow role was almost as boring as camping and required a smart team....sadly lacking in my CoD experiences. C2 was more arcadey and well...fun.
Least for me.
Hope this helps.
"Insurrection is the most sacred of the rights and the most idispensible of duties" - Marquis de La Fayette