interactive storytelling in games and experience

I was thinking about how games relate to interactive storytelling and I read in the book that a game designer's goal isn't to make a game but an experience and how they vary with each person. I began to remember when I had been talking with a few of my friends about Mass Effect 1 (slight spoilers ahead). I remember how one said that they had killed one of their teammates where as I later on refrained from doing so. I also recall how my brother had said that he had killed a club owner and later found the new party member who was trying to kill him. I, on the other hand, had found the party member first and when I had gone to confront the club owner, the party member killed the owner on his own. It was definitely interesting to see just how different the story was for each of us. I feel Mass Effect is a really good example of interactive storytelling tied with experience and how story progression can vary from player to player.