First of all, no one has the final say as to what is and what isn't art. Art is, more than almost anything else, the most subjective concept in the world.
A work of art is a thing that makes YOU, the viewer/reader/player/listener, feel something.
Therefore not every painting, sculpture, film, song, book, or game can automatically be called a work of art, because they may not necessarily make you feel something.
They can all be called artistic endeavors, as evoking emotion is their ostensible goal, but whether they achieve that is entirely up to you.
So guess what? Were you moved by the death of Aeris in Final Fantasy VII? that means that cutscene was a work of art.
Were you given to pause, if only briefly, before you pulled the trigger on The Boss in Snake Eater, because you were aware of the gravity and significance of Naked Snake's action? Well, that boss sequence looked very pretty, and had lots of artistic conceit about it, but it was that moment, every second that you hesitated to shoot The Boss, that was the work of art.
And I'm not even arguing that you can call an entire game a work of art because of one artistic moment it may have contained. All I'm saying is that we should recognize what actually makes a game art: Anything that moves you.