Ultimately, both games feature fantastic campaigns, easily some of the best in modern FPS games, but the 2024 Modern Warfare just edges it out by being a more polished and finished product.
As an example, the user claims that the visuals of MW were cleaner than MW2, and specifically compares the UI and HUD to Hulu and mobile games respectively. They state that using killstreaks was much faster in Modern Warfare, in addition to the smoother movement mechanics.