Mass Effect 2 (2010) begins two years later and sees Shepard's forces battling the Collectors, an alien race abducting human colonies to facilitate the Reapers' return.

The ending of Mass Effect 3 drew widespread criticism for being an unsatisfying conclusion to the trilogy, prompting Electronic Arts to release an expanded cut with additional cutscenes.

Over the next few decades, humanity is given access to new technology, allowing them to colonize new planets, and they are made part of the Citadel Security (C-Sec) forces, a highly regarded position that other species had been long waiting for and take resentment over.

After an Earth colony discovers a new Prothean artifact, it is attacked by an unknown vessel, and the Council names Shepard its first human SPECTRE (Special Tactics and Reconnaissance), an elite agent with associated authority and impunity, to investigate the incident.

They later fled from the Heleus Cluster three centuries before the arrival of the Milky Way races, when a protracted battle against an unknown enemy faction resulted in the usage of a weapon of mass destruction aboard a Jardaan space station.

After the Jardaan left, the Angara, genetically engineered creations of the elder race, began to develop their own civilization before falling under attack by the encroaching Kett.

With the Milky Way species' arrival, it becomes the responsibility of Pathfinder Ryder (who, like Shepard, is also customizable by the player) and their allies to shut down the malfunctioning terraforming systems, deal with the Kett and Angara attacks, and make planets habitable for colonization.

Both story and optional missions most often involve using their ship to travel via the mass relay to remote star systems and explore planets to find target objectives.

This is presented through what BioWare called a Dialogue Wheel, with the player-character reply options shown as choices extending radially outward from a circle at the bottom of the screen.

Mass Effect (2007), the first game in the series, was originally created as an exclusive title for the Xbox 360 but was later ported to Windows by Demiurge Studios in 2008, and to the PlayStation 3 by Edge of Reality in 2012.

The game focuses on the protagonist, Commander Shepard, and their quest to stop the rogue Spectre Saren Arterius from leading an army of sentient machines, called the Geth, to conquer the galaxy.

Seven episodic expansions were released as downloadable content, with Normandy Crash Site, Zaeed – The Price of Revenge, Firewalker, Kasumi – Stolen Memory, Overlord, and Lair of the Shadow Broker coming in 2010, followed by Arrival in 2011.

There were also five free DLC packs released for the multiplayer component, Resurgence, Rebellion, Earth, and Retaliation in 2012 and Reckoning in 2013, collectively adding thirty playable characters, dozens of new weapons and abilities, seven new maps, and a new enemy faction to complement the base game's three, among other content.

Set during the 29th century, the player's character is either Sara or Scott Ryder, designated as a Pathfinder – an operative tasked with discovering new planets in the Andromeda Galaxy on behalf of their species.

According to EA, "Every completed rescue and intelligence discovery in Infiltrator will increase a player's Galactic Readiness rating directly through the 'Galaxy at War' system in Mass Effect 3.

Through APEX HQ, players can view their progress in multiplayer, equip characters, assign skill points, manage Strike Teams, and access their friend list.

"[29] Due to Mass Effect 1's age, it received the most extensive work for the Legendary Edition, which BioWare compared it to the quality of a remake, while stating that the other two games were still remasters.

[102] In November 2024, Amazon officially announced the series was in development with Karim Zreik producing under his Cedar Tree Productions banner alongside Ari Arad and Michael Gamble of Electronic Arts.

[114] Based on the "underlying idea that real-life scientific discoveries consistently create imagery and concepts that blow away previous notions of what is possible," Hudson opined that "reality will continue to be stranger than fiction" which in his view justifies the developers' creative license with their work.

[114] A spin-off for the Nintendo DS titled Mass Effect: Corsair, patterned after the gameplay of Star Control and centered around a Han Solo-inspired space pirate character played from a first-person perspective was briefly explored in 2008.

[116][117] Former BioWare employee Dorian Kieken noted that the central concept of Corsair as a narrative adventure which follows a morally ambiguous protagonist would have been an ideal vehicle to explore as an expansion of the Mass Effect universe.

[114] Aspects of Greek mythology have been consistently invoked throughout the series, from the names of in-universe objects and organizations like the planet Elysium or the anthropocentric paramilitary group Cerberus, to the narrative themes of certain story arcs like the Prothean's connection to the contemporary civilizations of the galaxy through the technology they left behind.

[114][123] The music of the series is noted for its similarity in style to the vintage synthesizer score for Blade Runner, which creates a mood appropriate for the oscillating wonder and terror of unknown space.

[157] Tauriq Moosa from The Guardian lauded the Mass Effect franchise as some of the best science fiction ever made, describing its overarching theme of "aspiration and connection in the face of an indifferent cosmos" to be "as cerebral as Star Trek, as hopeful as Asimov and as dramatic as Battlestar Galactica".

[164] Kyle Munkittrick from Gizmodo argued that Mass Effect, based on several factors articulated in his article, is the most important science fiction universe of the contemporary generation.

[166] Cian Maher from TheGamer credited the series' well-written codex entries as playing an instrumental role in building "one of the most fascinating universes in the history of video games".

A cutscene from the first Mass Effect, which contains depictions of partial nudity and sexual activity, was accused by neoconservative media outlets of being obscene content in late 2007.

[145] Controversy over the cutscene, especially one version which depicts a potential intimate scene between Liara T'Soni and a female Commander Shepard, attracted at least one instance of government scrutiny, which led to the game being briefly banned in Singapore.

[177][178] The controversy prompted an intervention from BioWare management into the development of Mass Effect 2 to remove planned same sex romantic content for companion characters like Jacob Taylor and Jack.

[187] Other noteworthy controversies surrounding the series include public outrage over the alleged link between the series' in-game combat violence to the perpetrator of the Sandy Hook Elementary School shooting, which was later debunked;[188][189] the appropriation of assets from Mass Effect 2 into a propaganda video to support the 2016 presidential campaign of Donald Trump, which was promoted by Trump's social media accounts shortly before it was taken down over claims of copyright infringement by publisher EA;[190][191] and reactions to the portrayal and representation of women as well as sexual minorities.