It is the first game in the Mass Effect series, and takes place within the Milky Way galaxy in the year 2183, where civilization is threatened by a highly advanced machine race known as the Reapers.

The player assumes the role of Commander Shepard, an elite human soldier who must stop a rogue agent from carrying out the Reapers' galactic invasion.

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

[1] The game uses an over the shoulder perspective akin to a third-person shooter, and features a cover system which allows players to strategically hide behind objects while fighting enemy forces.

[1] The player may also issue orders to the squad members, such as sending them to take cover behind an object, scout ahead, regroup, or focus their fire on a designated target.

These points allow the player to develop talents that affect the availability of new special Paragon and Renegade dialogue options with significant impact in the game.

[10] The term "Mass Effect" is defined as a form of mass-negating technology, allowing the creation of physics phenomena, like artificial gravity or FTL travel.

[11] 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.

Shepard's squad members include human Systems Alliance marine Kaidan Alenko (Raphael Sbarge), human Systems Alliance soldier Ashley Williams (Kimberly Brooks), turian Citadel Security officer Garrus Vakarian (Brandon Keener), krogan mercenary Urdnot Wrex (Steven Barr), quarian mechanic Tali'Zorah (Ash Sroka), and asari exoarchaeologist Liara T'Soni (Ali Hillis).

The two discuss their victory while also mentioning an artifact called the "Conduit" and the return of the Reapers, a highly advanced machine race of synthetic-organic starships believed to eradicate organic civilizations every 50,000 years.

On the colony of Feros, Shepard acquires the ability to comprehend and interpret the images seen in the vision from a former subordinate of Benezia, and learns that Saren's flagship, Sovereign, possesses unique mind-control capabilities.

Sovereign reveals that the Reapers remain outside the galaxy waiting for organic life to develop and discover the Mass Relays, before harvesting them when they reach their peak of advancement.

Shepard presents this information to the Council, who dismiss the need for a mission to Ilos and instead opt to reinforce the military presence around the citadel in anticipation of Saren's offensive.

On Ilos, Shepard learns from a Prothean virtual intelligence (VI) named Vigil that the Citadel is actually an enormous Mass Relay that the Reapers use to invade the galaxy.

A few Protheans survived the last extinction cycle via cryopreservation on Ilos and then re-entered the Citadel via the Conduit, a reverse-engineered miniature Mass Relay disguised aboard the station as a statue.

[17] Mass Effect uses the Unreal Engine 3 as a groundwork, but on top of that the team developed additional components for advanced digital actors, space exploration, and squad combat, resulting in BioWare's largest programming project at the time.

[16] Because BioWare wanted to create a memorable story, Mass Effect was envisioned as the first chapter of a trilogy from the very beginning, and having a considerable technological basis would help shorten the development cycle of its future sequels.

[15] According to Hudson, this approach would allow them to create a unique "level of intensity and cinematic power", while at the same time give the player the same role-playing customization as previous BioWare games.

[29] One of the biggest challenges the writers faced was the amount of volume they were required to write to support the game's multiple dialogue paths and story outcomes.

The Limited Collector's Edition included a bonus disc of exclusive Mass Effect background material, a soundtrack, and design galleries featuring more than 600 pieces of artwork with full audio commentaries.

[54] Microsoft initially intended to use SecuROM, a digital rights management software which would require online activation after installation and additional authentication checks every ten days.

[59] Ryan Geddes of IGN highlighted the pack's included extras and "stunning" visuals,[61] while Dan Whitehead of Eurogamer criticized its lack of narrative weight and reuse of outpost maps that are also available in the base game.

[60][64] The pack introduces a training facility where the player can compete in eight virtual reality combat scenarios, divided into four different game types like Deathmatch and Capture the flag.

[1][73][80] Kevin VanOrd of GameSpot described Mass Effect as "a great game with moments of brilliance and a number of small but significant obstacles that hold it back from reaching its true potential.

"[1] Similarly, IGN's Erik Brudvig considered it greater than the sum of its parts, stating that although Mass Effect features numerous technical issues, most of the game "is so expertly delivered that it can transcend its weaknesses.

[69] Although the visuals were credited for their dramatic set pieces and evocative soundtrack, critics noted the game's inconsistent frame rate and long loading times.

[69] The galaxy exploration was favorably compared to the 1986 adventure game Starflight and the number of optional missions was highlighted positively,[70][76][83] but the Mako sections were disparaged for their rocky planetary design and clumsy combat mechanics.

[86] Mass Effect proceeded to sell over one million units worldwide within fewer than three weeks on shelves, according to Microsoft vice president Jeff Bell.

[88] In November 2008, the game's Xbox 360 version received a "Gold" certification from the Entertainment and Leisure Software Publishers Association, indicating lifetime sales of at least 200,000 copies in the United Kingdom.

The scene first came under scrutiny in an article by neoconservative blogger Kevin McCullough, who employed statements such as "Mass Effect can be customized to sodomise whatever, whomever, however, the game player wishes", and "with its over the net capabilities virtual orgasmic rape is just the push of a button away.