As you have probably already heard, film critic Robert Ebert recently took back his axiom that video games are not art. Because of this we are back at step one, are video games art. The only way we can classify something as art or not is if we have a universal definition of what art is, unfortunately this is easier said then done. Wikipedia defines art as "Art is the process or product of deliberately arranging elements in a way to affect the senses or emotions."
If we take the Wikipedia definition of art we could apply this to video games. My first example is Bioware's sci-fi RPG Mass Effect 2. Mass Effect 2 fulfills this definition because it does affect the player's senses and emotions. An example of this *spoilers ahead* is when your crew was abducted. Even if you hated your crew you still felt a sense of emptiness when you returned to your ship to find your entire crew gone.
I have a slightly different definition of what art is "Art is an experience created by an artist that expresses an idea or feeling.", Udunnojack has a very broad definition of what art is "Art is anything that required creativity to create.". Now we both consider that video games are art but for different reasons. Udunnojack says that all video games are art because the developers used creativity while making the game. I question that claim due to all the sports games that are exactly the same as the previous year's version with nothing new but a small new gimmick that changes nothing and new team rosters.
Due to my definition of what art is I believe that not all, but most video games are art. Most videos games express an idea or feeling. For example, in Call of Duty World at War it expresses the feelings of the losses suffered in war and shows the idea that millions of men and women died to protect something they loved. To me this is art. Is the multiplayer aspect of CoD: WaW still art? It does still express these ideas but to a lesser extent then the single player.
By my definition not all video games are art, yet to others all video games are art or no video games are art. This is the inherent problem with trying to classify video games as art. Until we get a universal definition of what art is then we will never be able to definitively say whether or not something is art.