Left4Dead2

This co-operative action horror FPS takes you and your friends through the cities, swamps and cemeteries of the Deep South, from Savannah to New Orleans across five expansive campaigns.
Left 4 Dead 2 is set during the aftermath of an apocalyptic pandemic, and focuses on four survivors fighting against hordes of the infected, who develop severe psychosis and exhibit zombie-like tendencies.

The survivors must fight their way through levels, interspersed with safe houses that act as checkpoints, with the goal of reaching a rescue vehicle at the campaign's finale.