I’ve never really considered a game to be an art form. Sure, the production of games and art is similar in that they are both a creative processes, but I’ve never thought that the intentions behind them were similar (art: to express, game: to win). I think that the idea of a game being art it is a relatively recent idea, which emerged out of conceptual art movements of the 20th century.
I think that in order for games to be considered art, the act of playing or the end result of playing must fulfill some conceptual goal, in the same way that finishing an artwork cements an idea or a goal. The methods/guidelines for this goal are obviously quite ambiguous and are part of the creative process.
Another similarity between an art-game and more traditional artwork is in the variables that exist within their respective processes. The results of both are dependent on variables such as: circumstance, personality and skill.
But despite common variables, the main difference between the two is still chance. Chance is what consumes games and is what makes them what they are, while the ideal in traditional artworks is more often than not, to remove chance.