With Tetris, what do you need? Quick fingers and fast reflexes. I look at it the same way Lise & Lil Me do. Somewhat impressed, but I think they should be doing something better with their time.
But with something like Dance Dance Revolution, at least the player is getting some exercise, and actually impresses the people, because the audience can appreciate the fact that they have to be in shape / have good coordination / rhythm / etc. in order to do those dances. A *better* use of time than playing Tetris.