Besides the moment-to-moment shooting, what's the one thing that's made Call of Duty the success that it is today? If you ask me, it's the progression. You level up your account, unlocking new guns as you go, which pulls you into the camo grind, all for you to prestige and do it all over again. It's a dopamine rush that worms its way deep into your brain. I still remember the incredibly obnoxious (but admittedly cool) level-up sounds from the original Modern Warfare trilogy era...
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