At first, I wasn't a big fan of Mass Effect. I didnt understand the gameplay, and I wasn't paying attention to the characters and plot overall. Little did I know, that those are the basis on which Mass Effect is built on.
The thing that brought me back to ME now that I think of it was the fact that your choices actually get directly imported to the sequel. This premise interested me, and I gave ME another shot. What I found was something spectacular.
What I persoally liked about ME, ME2, and ME3 is the fact that the characters and story are unlike anything else. I get that if you aren't into Science Fiction, it is probably not very interesting. That said, the whole story is woven together extremely well, better than any other gaming story that I know of (save for the ending of 3 in some respects). Along with that is the lore. If you want to know something about a specific alien race, or a war that happened prior to the game, you have a way to find out. The access of that information lets people, like me, get invested in whats going on. Before you know it, you begin to care about what is happening and who its happening to.
This is also amplified by the brilliant characters. They built a cast that people can get attatched to, or even hate. Its up to you to decide who you like and who you dont like, and your reasons are all based on how you are as a person. Some people love Ashley because of her love of God and poetry. Others hate her because they think she's racist against non-human races. The fact that this kind of discussion can be had between players just helps people get invested even more.
The friendship that most people develop with the mainstay characters, like Tali and Garrus are phenominal. By the time you get to the third game, you feel like you truly have been through it all with these characters, and they respond to it. Find any other game that does that in the way that Mass Effect does, because I don't know of it. The writing is so great in fact, that side characters that you meet on a whim become memorable because of what they have been through. Along with that, when you do run into these side characters in the sequels, it makes it all the more special.
Mass Effect is great to me because of the ways that you get attatched to the characters. Learning about their past, fighting with them, sharing humerous and serious moments with them, they make them seem real to me. Garrus and Tali are some of my favorite characters in gaming because of that. I cant think of any other experience in any other media that has the same kind of connection that I helped influence.
Idk about anyone else, but thats why I'm emotionally connected to Mass Effect