Art games are games where one player plays all the moves for both sides, playing the best moves they can find. Since one player is playing all the moves, the goal is not to win, but to create a beautiful game record: a work of art.
The beauty of a good artgame is understated. A beautiful art game doesn't come from setting up the most devastating tesuji: if the player can read out a devastating tesuji, they could have played moves (as the other color) to prevent that tesuji. Thus a lot of the beauty of an art game is not in the game itself, but in the variations that were prevented.