Mass Effect 2 is a role-playing game with an outer space, science fiction setting and action-oriented, third-person shooter play. The game is released as the second in a planned trilogy from BioWare, designed for Xbox 360 and Windows-based home computers. Players resume the role of Commander Shepard, the customizable protagonist of the first game, choosing the hero's gender, appearance, skills, and abilities to match personal preferences and playing styles. Combat is squad-based, as in the original game, and players may choose their teammates from a roster of stealthy assassins, superhumanly strong warriors, and brilliant masters of mystical powers. The game's main quest is seen as a suicide mission, so assembling a team that is not only able but also willing to follow Shepard into the dangerous unknown of deep space remains a role-playing challenge throughout the adventure.

Mass Effect 2's continuing story involves the appearance of a race of insect-like humanoids, which seems to have been abducting entire colonies of humans from the fringes of known space. To investigate this new threat, Shepard works in league with the ruthless Cerberus organization, a powerful and secretive group whose only morality is the survival of the human species, at any cost. Although anyone is free to create a new character and make a fresh start in the game, players who completed the original Mass Effect may use save files to continue their adventures in the sequel, using the same customized version of the hero they led through the first game. Similarly, the outcome of the final mission of Mass Effect 2 may influence players' options as they begin the final game in the trilogy, whether Shepard remains to lead another mission against all odds, or is remembered as a brave warrior who made the ultimate sacrifice for the sake of all humanity.