“Old” call of duty is based from WWII, which were made in the early 2000s inspired by Medal of Honor while “New” call of duty is the fictionalized takes within the FPS genre (basically the ones you recognize today). Modern Warfare (the 2007 one) is the title that departed from the WWII genre while World at War tackled at both theaters of WWII (the Pacific and European).
I’m personally a big fan of movement penalties in shooters, that prevent people from breaking their momentum in a flash, jumping or dropping instantly, etc. They feel slightly frustrating to control, but it comes back in how easy it is to aim at someone.
It’s really frustrating when you’ve outflanked someone, and have a strong gun against them, but their A/D crouching game is on point.