The player assumes the role of Commander Shepard, an elite human soldier who must assemble and gain the loyalty of a diverse team to stop the Collectors in a suicide mission.

[1] Battles take place in real-time, but the player can pause the action at any time to calmly target enemies and select different powers for the squad members to use.

[5] The player may also issue commands to the squad members, such as sending them to take cover behind a manually picked object or focus their fire on a designated target.

For example, armour is usually vulnerable to powers such as Incinerate, which burns enemies over time, and weapons with a low rate of fire, such as sniper rifles and heavy pistols.

[12] A conglomerate body of governments known as the Citadel Council controls a large percentage of the galaxy and is responsible for maintaining law and order among races of the galactic community.

[14] During the events of the original Mass Effect, a geth army attempted to open a portal for the Reapers, a highly advanced machine race of synthetic-organic starships that are believed to eradicate all organic civilization every 50,000 years.

Shepard's squad members include Cerberus operatives Jacob Taylor (Adam Lazarre-White) and Miranda Lawson (Yvonne Strahovski), recurring associates Garrus Vakarian (Brandon Keener) and Tali'Zorah (Liz Sroka), salarian scientist Mordin Solus (Michael Beattie), human criminal Jack (Courtenay Taylor), genetically engineered krogan super soldier Grunt (Steve Blum), drell assassin Thane Krios (Keythe Farley), asari Justicar Samara (Maggie Baird) or Samara's serial killer daughter Morinth (Natalia Cigliuti), and geth mobile platform Legion (D. C. Douglas).

[17] In 2183, shortly after the events of Mass Effect, the SSV Normandy, while patrolling for geth resistance, is attacked by an unknown vessel, forcing the crew to abandon ship.

[18] The body is pulled into the orbit of a nearby planet and recovered by Cerberus, who begins the "Lazarus Project" with the sole purpose of bringing Shepard back to life.

Escaping alongside Jacob Taylor and Miranda Lawson, Shepard is brought to meet the Illusive Man, who reveals that entire populations of human colonies have disappeared all over the galaxy.

[20] Before actual production began, BioWare created a list of goals to work towards based on feedback from fans, reviewers, and internal staff members.

[20] According to lead designer Christina Norman, "we wanted more satisfying combat and a big part of that is making weapons more accurate and powerful at level one—basically saying 'let's take the RPG out of the shooter.

'"[20] Since BioWare had no experience with shooter games, the team spent roughly three months tuning how combat would work using the original Mass Effect as a basis.

[20] Real-time gameplay with an emphasis on weapons and cover was a preference because the team felt that the constant pausing to select powers interrupts the intensity of the combat.

[23] As Hudson explained, "Our writers write into a dialogue editor and that becomes fused with the way that you end up seeing many different pieces of Matinee play out in combination when you have a conversation with characters.

[23] Hudson mentioned two significant challenges that interfered with the development: financial problems due to the Great Recession limited the game's budget, and the team had to get through it without impacting their ambitious goals.

[38][39] The score also features some pieces by Sam Hulick, David Kates, and Jimmy Hinson (better known as Big Giant Circles), with additional editing and in-game implementation by Brian DiDomenico.

[54] Players could also redeem codes on specially marked Dr Pepper products for one of three pieces of headgear[55] and registered copies of Dragon Age: Origins for a new armour set.

[61] The collector's edition featured a different packaging, an artbook, bonus in-game content, a behind-the-scenes DVD, and one issue from the Mass Effect: Redemption comic series.

[2] Tom Bramwell of Eurogamer positively highlighted the weight of social interaction on the outcome of events and that players feel actual pressure for their decisions.

Edge credited them for their complex personalities and great characterization,[95] while GameRevolution pointed out that the loyalty missions "reach deep enough into their characters to make you empathize with all of them".

[5] He wrote that "deep reds and glowing indigos saturate certain scenes, making them richer and more sinister; eerie fog limits your vision in one side mission, while rain pours down upon you in another.

"[5] Reviewer Adriaan den Ouden of RPGamer credited the conversations and cutscenes for featuring better cinematography than the first game, stating that "it's hard to imagine them becoming much better in Mass Effect 3".

[106] Critics also gave high marks to the game's extensive cast of voices; in particular, Martin Sheen's performance of the Illusive Man, which was singled out for "steal[ing] the show".

[2][5][96][102] John Davison of GamePro wrote, "BioWare has done a spectacular job moving the role playing genre forward, and blending disparate gameplay styles into genuinely exciting sci-fi epic.

[102] Jeremy Parish of 1UP.com credited the combat for being more balanced, stating that the game encourages players to use different weapon classes and squad abilities when the situation requires it.

"[101] He also remarked that the PlayStation 3 version suffers from technical issues such as frame rate inconsistencies, graphical glitches, and other minor bugs, mostly present in the downloadable content sections of the game.

[101] Game Informer reviewer Joe Juba reacted negatively to the lack of save importation from the original Mass Effect, which was initially not released on PlayStation 3, and pointed out that the decisions made in the Genesis comic "have practically no context".

GamesRadar editor Hollander Cooper explained that the game improved the technical issues of its predecessor significantly while at the same time "expanding the already-impressive universe without sacrificing what made the series special.

[122] Eurogamer editor Rick Lane described Mass Effect 2 as a darker, warmer, and overall more human game than its predecessor, noting that it is the player's responsibility to make sure these characters are prepared for the final mission, or they will die.