Story? Oh woe is me humanity is being beat to shit by all these invaders even though we have millions of soldiers that kick ass and can revive an infinite number of times instead of dying? Oh look at this beautiful city it's our last bastion all of humanity's hopes too bad you get stuck in one tiny, barren section of it and don't get to see any semblance of actual human life. Oh look at all those bad aliens hogging our beautiful planet Earth let's go teach them a lesson and take it back even though the place is a wreck and the constant respawning enemies and empty, constricted landscapes make it feel like you're fighting over a tiny landfill with a pack of stray dogs.