Helldivers 2

The gameplay itself is in missions where it's up to 4 of you, co-op, against the enemy hordes. Sometimes you're trying to blow up an enemy installation, or launch a missile, or whatever. About 40 minutes or less where there's only 4 "good guys"

The part where it feels like worldwide co-op is that every mission someone wins or fails contributes to the shared global conflict. So we all have some order to defend a planet that is under siege by our enemies, and so the community all does missions on that planet to attempt to rescue it from the attack, etc.

Its 4-player coop in-mission, but there is a meta-game where the entire community contributes towards spreading or defending democracy across several planets neighboring super-earth. So this week one faction might have gained some ground, so everyone is encouraged to fight on that front, but the next week there might be an order to push back the border of the opposite faction. I believe there is one person, Joel, who is in charge of playing dungeon master for the overarching war.

At a player level, the status of the war will determine which planets are available to do missions on and what your personal challenges will be set to (to reward you for contributing to the cause). This updates on a near daily cycle and adds a bunch of great variety to the environments and challenges you'll face.

Kind of. It takes 10s of thousands of players to liberate a planet. And everybody gets rewarded when specific planets are liberated within a timeframe. Or punished if we fail. Last time we all got mechs. If we had lost the enemy would have gotten the mechs. So to win the wars a significant part of the player base has to focus on specific targets otherwise the enemy gets stronger and move closer to Super Earth.