More recent entries into the genre have added things like campaign modes, loadouts, or RPG-like progression mechanics like weapon unlocks and character class leveling to keep players coming back for more.
The basic formula is simple - take the level-based horde mode popularized in games like Gears of War and then add a light coat of story and some linear level traversal to tie it all together. The release of Back 4 Bloodmarks yet another entry into the cooperative multiplayer shooter category, a genre that owes its popularity, in large part, to the huge success of developer Turtle Rock Studio’s other series, the legendary Left 4 Dead and its sequel.
