That's really hard, because you can barely say anything without spoilers. You might want to get him to read the book Mass Effect: Revelation. It's a great book that gives an introduction into the Mass Effect universe without actually spoiling any of it. I don't know what else to say, Commander Shepard is awesome and he goes and and fights the bad guys? Not only is that a breathtaking simplification, it's spoiling the game just by mentioning one of those bad guys. It's just so complicated. I think that book would be a great introduction.