The first-person shooter game genre has done relatively well for itself in the nearly two decades it’s been around. From “Doom” to “Duke Nukem 3D” to “Half Life” to “Crysis,” it seems that any action-oriented game that involves shooting at mutants, aliens or other ugly entities falls into either the FPS category or its close cousin, the third-person shooter. Unlike those eggheaded strategy games that require constant consultations with phonebook-sized manuals, there’s almost no learning curve for an FPS. What button is shoot? What button is move? OK, go play now.