The idea that video games are the only interactive art form is patently ridiculous. If novels, paintings, film and theater were not interactive we would not enjoy them even a little bit. The fact that you as the audience or reader are constantly reconstructing and reorganizing the narrative, judging the characters, wondering what will happen next...these are all the things that make these art forms what they are. Video games merely extend this process into the literal.
by that logic, a bird in flight, completely beyond my power, is interactive. I can wonder where it came from, where it's going, condemn it as unintelligent or worship its freedom from human "rationality." This doesn't make the bird interactive, it only means that I am alive and that my perception of the world's output is subjective.
videogames, on the other hand, are one of few art forms (there is an excessive amount of interactive installation and performance art that was forgotten in the list) where the users input changes the output. That is a dramatic and vital difference and it's both an expanding and a limiting factor depending on the context.
That's a pretty crazy stretch 
Film of a bird in flight in the context of an entire film, or a painting of a bird in flight, is to me VERY different from simply seeing a bird outside, because there is a director or a photographer or a painter interpreting and changing it and showing it to us in their own way. Viewing or consumption of artistic works IS interactive in a way that passive observation of natural phenomena is not. And of course, video games are interactive in a way that other art forms are not, I wholeheartedly agree.
My point is simply that the idea that games can't be art because they are interactive just rings very false to me. They are *more* interactive, that's all. The idea of arbitrarily drawing a line in the interactive sand is just crazy, and I've never understood Ebert's reasoning behind it.
About Ebert: don't care, he's an old film buff, he's not expected to like or understand or support a competing, different art form.
About videogames being art: of course they are, anything that is not (or is not considered) completely utilitarian and constrained by external forces has a spark of artistic expression from the person who decided to do it like that and not differently.
Being something that is produced from the ground up as a source of designed experiences for the public, videogames can be classified along with older art forms like painting, sculpture and music at the purest end of the spectrum of art forms.
About interactivity: I side with ndchristie, you are confusing
interpretation, that takes place entirely in the observer's head,
interactivity, which affects the artwork (or at least its temporary manifestations), and merely intentionally directing the observer's
attention without causing changes.
About the bird example: an actual bird might be beautiful, but isn't art because we know it is not the work of someone (barring aberrant cases, like suspecting it's actually been put there for our entertainment); a bird film is art, albeit probably boring, unless we are convinced that it is utterly meaningless (for example, it's a byproduct of testing an automatic motion-activated camera system with birds on a sky background; but even that would have some art "margin" left, such as the choice of camera placement, time of day etc.).
