On November 16, 2007, more than a million people set out on what would be a five year journey through the cold emptiness of space. Along the way, they would meet countless aliens and forge long-lasting relationships of every kind, become a flawless paragon that others would aspire to be or a ruthless renegade who leads through fear or anything in between, and face down an existential threat that would devour all life in the galaxy if given the chance. By March 2012, at the end of an era, the final chapter of Commander Shepard's story (for now, at least) was to be written by almost 4 million people in Mass Effect 3, each with their own stories of sacrifice, misguided heroism, and even lust.
With such a large audience, BioWare had to make sure that the final part of Shepard's story arc was virtually perfect. Fortunately for them, they could build upon all the feedback that they had received on their previous games, not just games from the Mass Effect series. Furthermore, the technical limitations of the various platforms at the time were fairly well understood, meaning that the team mostly had to concentrate on gameplay and storytelling, at least according to BioWare Edmonton's General Manager Aaron Flynn. Likely as a result of this, Mass Effect 3 was the first game in the series to feature any kind of multiplayer, which proved to be very positively received (it certainly didn't hurt that there was free DLC involved).
Given that Mass Effect 3 built upon the backstory of two other games, however, it was inevitable that there would be an influx of new and returning players who may not be entirely up to speed with the adventures of Commander Shepard. In an attempt to combat this, BioWare's writing team treated the game as a movie, trying to make it as accessible as possible so that people would "just be able to jump in." On top of that, writers were given the responsibility of creating individual missions, which would then be reviewed by the rest of the writing team.
As effective as this method may have been in crafting the overall story of Mass Effect 3, it would be remiss to not mention how disliked the ending of the game was (among other plot-related things). In the days, weeks, and months following the release of Mass Effect 3, fans went through every stage of grief over the fate of their Commander Shepard, which was rather understandable given the situation. For many, having years of virtual relationships, conquests, and achievements converge into three rather bland choices that more or less ignored all of your past actions was too much to bear. Some even went so far as to craft elaborate theories that, in short, hypothesized that Mass Effect 2 and 3 followed the actions (or rather, hallucinations) of a brainwashed Commander Shepard. Needless to say, BioWare shot down these theories. Though, to their credit, they were aware of the complaints that people had; at least two DLCs (the Extended Cut and Citadel) gave people some of the closure that they were originally expecting with their characters.
With the upcoming release of Mass Effect: Andromeda, and all of the cautious excitement surrounding it, it would be safe to say that most rational people have forgiven BioWare for Mass Effect 3's ending. If anything, Mass Effect 3 proved that compelling storytelling on a more personal level can make up for almost anything, and that people, despite all of their complaints, enjoyed their interplanetary adventure not because of where it led, but rather because of who they met along the way.