The summer after my sophomore year, I picked up a used copy of "Mass Effect". I'd heard a ton about it, but had never spent any time playing through the system. In a nutshell, the game is an action sci-fi about a character, Commander Shepard, who can be male or female based on early character creation. In the future of the human race, we find a whole plethora of other species and live alongside them in the galactic communities. In the first game, Shepard is sent after a rogue agent named "Saren" of a different species who is trying to take over the galaxy with a race of self-thinking robots called the Geth. We find later that Saren has been brainwashed by a race of superior synthetic beings called the Reapers, and the fight turns to them as the bad guy. Through games two and three, Shepard and the other races struggle to survive in the face of these superior beings.
What was interesting about this series, was it was open-galaxy sandbox style game. As you met characters, made choices about which missions to undertake, spoke with characters throughout the games, and ended missions in certain ways with huge decisions affecting the future of certain characters or species, the game adapted with you. At the end of game one, there had been several hundred decisions, all of which affected which characters lived, died, or what their life trajectory was. Enter game 2, and all of those choices were imported and the timeline continued. Time and time again you saw choices you made in the previous game affecting your current one. Characters who died in game 1, were suddenly not present in game 2. At the end of game 2, all the choices of game 1 AND 2 were imported into game 3.