I've always considered video games as a medium capable of being art. Not all games are, of course, but the same could be said of any other medium. Some movies are garbage and if I scribble a few paint lines on a canvas, it doesn't make it a work of art (It takes a whole 'nother level of pretentiousness for that! *zing*)

More on topic though, what would you consider the most important aspect of a work of art? Maybe you think differently, but to me, the single most important aspect of a work of art is the ability to inspire emotion. Video games are the medium with the most potential to do this. No other medium is as interative as a video game and no other medium can draw the viewer - player in this case - into it like a video game can. Done well, the emotions inspired by video games can be far more personal. Far more powerful. And this is because as the player rather than as just a passive oberserver, you are playing an active role.

Maybe the extent of the emotional impact is frustration or rage at a difficult section. Joy of accomplishment or anticipation of something to come. However, those are fairly shallow and easy to come by. Most games pull that sort of thing off without much effort. Consider instead the sort of game with a deep plot and interesting characters. The sort that draws you into the world and makes you empathize with the protagonists. Makes you feel their joy and experience their sorrow (For me, the first one to come to mind is always Final Fantasy VI). That is true art. Anyone who questions the validity of video games as art, I ask you how is that any less valid than a novel or film that does the same?