As BioWare designed the game to be accessible to both old and new players, many of the series' traditional gameplay elements remain, such as cover-based third-person shooting, but new aspects are introduced as well, such as a multiplayer component.

[13] Unless it is set to Action Mode, the player interacts with non-player characters in Mass Effect 3 by using a radial command menu where dialog options depend on wheel direction.

For example, if the player encounters an Atlas Mech and defeats its driver without destroying the entire suit, Shepard can climb inside and take control of its heavy-duty weaponry.

[38] The galactic community lives in fear of an invasion by Reapers, a highly advanced machine race of synthetic-organic starships that are believed to eradicate all organic civilization every 50,000 years.

[43] While the exact roster can vary,[2] Shepard's squad members generally include Systems Alliance officers Ashley Williams (Kimberly Brooks) or Kaidan Alenko (Raphael Sbarge), Systems Alliance marine James Vega (Freddie Prinze Jr.), asari information broker and researcher Liara T'Soni (Ali Hillis), turian military adviser Garrus Vakarian (Brandon Keener), the Normandy's artificial intelligence EDI (Tricia Helfer), and quarian engineer Tali'Zorah (Ash Sroka).

[44] Other characters include Systems Alliance admirals David Anderson (Keith David) and Steven Hackett (Lance Henriksen), Normandy pilot Jeff "Joker" Moreau (Seth Green), Cerberus leader the Illusive Man (Martin Sheen), Cerberus assassin Kai Leng (Troy Baker), Citadel Security (C-Sec) Commander Armando-Owen Bailey (Michael Hogan), and Asari crime boss Aria T'Loak (Carrie-Anne Moss).

[43] Certain characters such as human Cerberus officer Miranda Lawson (Yvonne Strahovski), salarian scientist Mordin Solus (William Salyers), krogan leader Urdnot Wrex (Steven Barr), human criminal Jack (Courtenay Taylor), genetically engineered krogan soldier Grunt (Steve Blum), drell assassin Thane Krios (Keythe Farley), asari Justicar Samara (Maggie Baird), and geth mobile platform Legion (D. C. Douglas) may appear depending on whether or not they survived the events of previous games.

Shepard must ultimately decide whether to allow the cure to proceed, in which case the salarian scientist sacrifices himself to deploy a counter-measure, resulting in a pledge of support from the krogan.

Following the events on Tuchanka and a failed coup by Cerberus to take over the Citadel, the quarians offer their support to the Alliance if Shepard helps them reclaim their homeworld, Rannoch, from the geth.

Desperate to reclaim Vendetta, Shepard's crew follow Leng to the Sanctuary facility on the human colony world Horizon, where Cerberus has been secretly researching Reaper-control technology.

[59] Shepard reaches the central base, kills Leng, and learns from Vendetta that the Catalyst is the Citadel itself, which the Reapers have captured after successfully indoctrinating the Illusive Man, who abandoned the station prior to the assault.

The ultimate fates of Shepard, the Normandy crew, Earth, and the rest of the galaxy depend on the player's choice in dealing with the Catalyst as well as their final EMS score.

[62] Similar to previous installments in the series, the game was directed by Casey Hudson, who originally created the franchise along with BioWare founders Greg Zeschuk and Ray Muzyka.

[72] The company also aimed to make the battlefield less predictable by introducing unexpected events and redirects, such as the floor giving out and the player falling to a completely different level of the environment, so that enemy encounters would not always go as telegraphed.

[79] Although Mass Effect 3 was originally planned as a project that could be finished in under two years,[67] by March 2011, it was clear that more development time was required, so BioWare moved the game's release date from Q4 2011 to Q1 2012.

[82] Because prior games allowed players to choose from different outcomes, the writers had to account for many possible variables; however, in anticipation of this challenge, they preemptively locked in certain story arcs to ensure that all Mass Effect 3 playthroughs had at least some commonalities.

[84] Mass Effect 3 offers expanded content, in comparison to prior entries in the series, for players who are interested in having their Shepard pursue same-sex relationships with non-player characters.

[85] It is also the first game of the series to offer an exclusively gay male and lesbian romance option, with shuttlecraft pilot Steve Cortez and communications specialist Samantha Traynor, respectively.

[87] In November 2011, a private beta of Mass Effect 3 was leaked onto Xbox Live, which allowed players to access unreleased plot details, and forced BioWare to alter some aspects of the story at the last minute.

[117] One pack, Extended Cut, expands upon the game's original endings with an additional choice to refuse the Catalyst, which inevitably results in a Reaper victory over the current cycle of organics.

[122] An interactive comic called Genesis 2 is also available for purchase and allows players to quickly customize important story decisions on the spot instead of having to replay prior installments.

[134] Tom Francis of PC Gamer (US) remarked that the finale was a "mixed bag", but ultimately praised its scale and emotional impact, which he felt was more satisfying than its main plot.

Discussing combat for IGN, Colin Moriarty observed that while changes from prior installments were minor, they were still evident, and anticipated that multiplayer would give the game added replay value.

[134] In an otherwise enthusiastic write-up for GameSpot, Kevin VanOrd recounted numerous glitches during combat, such as party members putting themselves in the line of fire by climbing onto crates and enemies getting stuck on walls.

[149][150] Kevin VanOrd of GameSpot and Craig Takeuchi of the Georgia Straight highlighted instances of dismissive comments against the game's same-sex relationship content which were posted on several websites in their respective articles.

[149][150] Queerty suggested that some of the user-generated comments posted on Metacritic were indicative of a review bomb movement to intentionally lower the game's user rating in response to the romance content.

[151] In April 2012, Jeff Brown, VP of corporate communications at EA, claimed that his company was inundated by "several thousand" letters and emails protesting the inclusion of LGBT content in the video games it publishes like Mass Effect 3.

[152] Other noteworthy controversies surrounding Mass Effect 3 included accusations of questionable business practices over the decision to release From Ashes as paid day one DLC;[153] allegations of conflict of interest involving the casting of video game media personality Jessica Chobot as an in-game character named Diana Allers;[154] the creative decision to utilize a stock photo as the basis of Tali's face;[155] and the online poll to determine the redesigned default appearance of a female Shepard.

[176] In 2018, Lucy O'Brien of IGN posited that BioWare's cooperative response to "Retake Mass Effect" contributed to a paradigm shift in how consumers influence video game developers.

[184] Mass Effect 3 was also identified by VentureBeat as one of the defining games of the 2010s due to the "firestorm of fans, press, and developers converging into an absolute mess of internet culture" over its ending, and its multiplayer mode, which ultimately became an unexpected monetary success.