I've long said that the mark of a truly great game is that it can make you extremely angry. Just look at any of other types of great games. Remember how mad you used to get at, say, Tetris, or Super Mario Brothers, or poker or any number of other great games. You get emotionally involved in them, deeply, and when things go against you, it just makes you angry. Human nature, coupled with immersion. My .02 anyway, and I've been saying that about games for years. I remember some years ago when a group of good friends and I used to play Magic the Gathering a lot. People would get so angry there would be actual shouting matches over fine points of the rules. Not that we weren't all still close friends, but a really good game has the capacity to infuriate you.