I've only played CoD2, a little of singleplayer CoD4 and a little CoD5 national socialist zombies.
CoD2 was alright, but sometimes it was confusing as to where to go, and I wondered what happened to my team mates often.
CoD4 was stuff. It took like 3 shots for you to die, and this is like loving modern day where you have BULLET PROOF VESTS.
CoD5 zombies was fun. I quote from Inglorious Bastards,
"We're in the killin' national socialist business, and cousin, business is a boomin'."