While gameplay among both games is largely unchanged, the compilation offers new game modes for each.
III includes an unlockable "extreme'" mode, featuring stronger enemies and a smaller blast radius on the players' shotguns. In exchange are faster reload time and a melee attack to evade damage from enemies and bosses (requiring the player to reload after use). X-Play stated that the ports are officially taken from the PC versions.
An exclusive mini-game happens when players switch from III to 2: protagonists Lisa Rogan and "G" bid them farewell as they enter an elevator, which travels back to the years 2015, 2010, and 2005. At each year, the elevator stops; the doors open to reveal hordes of zombies. Players earn bonus items for Original Mode by killing zombies before the elevator doors close. At 2000, the final stop, AMS agents James Taylor and Gary Stewart are shown preparing to face the horde (thus setting the events of 2 in motion).