"No one in or out of the field has ever been able to cite a game worthy of comparison with the great poets, filmmakers, novelists and poets."
So? Is it the quality of the work that decides whether it's art or not? He's got a very conservative opinion on what art is. I think most things that are made to stir some emotions in you can be considered art, even though they are shit. Some people can marvel at a blue dot on the wall, some people can listen to music which is basically sounds like a bunch of orchestras tuning their instruments loudly at the same time. It's silly for Ebert to dismiss video games as art because he thinks the quality is bad.
"One obvious difference between art and games is that you can win a game. It has rules, points, objectives, and an outcome. Santiago might cite a immersive game without points or rules, but I would say then it ceases to be a game and becomes a representation of a story, a novel, a play, dance, a film. Those are things you cannot win; you can only experience them."
From the article, this is the only thing that makes sense to me, and if I understand him correctly, this is the only argument he needs to dismiss games as art. In his definition a game per se cannot be art, because you have rules, objectives and you can win or lose. With that definition, I can agree that video games aren't art themselves, but they contain massive amounts of art, since they incorporate almost every other form of art.
Personally, I don't care whether they are called art or not. To me that term doesn't guarantee quality for my taste. But I do hope that people who contribute to making epic games will get recognition for their work. Video games still suffer from the stigma of being simple, brainwashing entertainment for kids and asocial nerds, mostly among our elite elders.