I love EU because of many things... Partly the unrivalled strategic gameplay, partly building up a nation and leading it to greatness, partly seeing the world spring to life and sometimes doing odd, but plausible things, and partly because I adore modding. I think I have at least spent as much time modding EU as I have spent playing it. And when you play the game then the game is not just over in thirty minutes or an hour, it is great. A game can take a month depending on how much you play per day. It makes the game feel epic and grand. It feels like you are rewriting history.
I do not know how I would explain that to a friend, but I did explain CK to one of my friends at one point. Although, I do not remember how I won him over to the dark side.