The games in the series are connected through the characters, events, and themes that are introduced in each installment. The story arc begins with Call of Duty 4: Modern Warfare, continues with Modern Warfare 2 and concludes with Modern Warfare 3.
Its single-player is flat-out terrible, its Zombies mode is uninspired, and its multiplayer has so many serious problems that it's hard to enjoy it. The game also has technical issues, and microtransactions that border on being pay-to-win because of how hard it is to spot paid skins in its maps.