(CNN) -- The widely anticipated "Mass Effect 3" will be the culmination of a story spanning a galaxy and eight years of development and drawing millions of fans around the world.
In the third and final installment of the series, set for release Tuesday, protagonist Commander Shepard returns for a battle to retake Earth from an advanced race of synthetics, known as Reapers, who want to cleanse the Milky Way of all intelligent organic life.
Developers from BioWare had always planned the series as a trilogy, so everything from the first two games has been leading up to this climax.
"On one hand, we knew where things were going so we could build these huge story arcs in the first one, and even in the second one, that would get resolved in the third game," said Casey Hudson, executive producer of the "Mass Effect" series. "At the same time, we were able to be pretty flexible in developing it mechanically so that as we started to really like certain story arcs and characters, we could build those in more and let players get more enjoyment out of playing."
But the question now becomes -- how to satisfy a fan base already engaged with the story's lore while remaining accessible to players who may just be meeting Shepard in the "Mass Effect" universe?
Fans of the science fiction/fantasy genre are familiar with how trilogies end. Whether it is Darth Vader tossing the emperor off a balcony or Gollum falling into the lava and destroying the One Ring, you can be sure of two things: Really big things are going to happen, and there will be a dramatic twist at the end.
Hudson said the way the "Mass Effect" series is built allows experienced players to continue with the stories they've already worked on but also provides entry points for new players to get quickly acclimated to the tale and begin their own adventure. As with "Mass Effect 2," players who have saved characters will be able to import them into "Mass Effect 3," changing some dialogue (the game will have a hefty 40,000 lines) and missions to reflect actions taken in previous games.
New players are quickly brought up to speed through some introductory missions and different dialogue from experienced characters. But Hudson said new players shouldn't feel like they are missing out on anything.
"The fact that it is a third story means that's where you get to decide the fate of entire civilizations because we know this is the third of three," he said. "If you are coming in as a new player, those plot lines are established, but you also get to make the biggest decisions in them. For existing players, it's mind-blowing that they've gotten to know people and characters from a given species that they can choose to wipe out in 'Mass Effect 3.' "
He added, "That was the real fun of developing 'Mass Effect 3.' This is the beginning of all the biggest things you get to do in the 'Mass Effect' series, and then everything comes to an end that you define as a player."
Defining the parameters of the story and possibilities for the ending pushed the limits of Hudson's team, he said. Since it's the final episode, everything needs to get resolved and all lingering questions answered.
Hudson said that despite players being in the driver's seat, they want to see that developers have created interesting and satisfying conclusions of the story arcs in which they've become invested.
Which species will live and which will die? Which major character doesn't make it to the end, and who will be left for the final battle? Players, new and veteran, will both have those choices to make and be saddled with the emotional baggage that goes along with it.
"The team was really pushing to put little bits of fun even in the final days. (The game) ended up being bigger than what we thought it would be," Hudson said. "Whether you are a really passionate fan about the fiction or you're fairly casual about it or you're new to it, it should be a great story for everybody. We tried to build it as a story regardless of how familiar you are with the 'Mass Effect' universe.
"This is really the biggest part of this series. That's what the whole story's about."
"Mass Effect 3" will be available Tuesday in North America, Thursday in Australia, March 9 in Europe and March 15 in Japan. It is playable on the Xbox 360, PlayStation 360 and Windows PC. It currently does not have a rating from the Entertainment Software Rating Board.