I'd say that games already should be considered art, both directly and indirectly. You just have to look at it from an angle that is not traditional art.

When you look at it 'directly' as art, think of the special eye candy screenshots that are taken to show how beautiful scenes can look. Or more simply, think about the wallpapers that are made officially from the game. Look at this as an example and I can't imagine any other word to describe it than 'art'.

Indirectly speaking a popular game will spawn fan art, fan fiction, official novels and so on. The majority of these things are definately peices of art.