Jason VandenBerghe makes a good point here that the art of games is present in the gameplay. The problem is he suggests that it's ONLY in the gameplay, and not in the creation of the thing played. This was my response in his comments, posted here and on my personal blog so that people can respond separately at greater length if they choose.
What about music?
The performance is art.
The instrument is art.
The composition (the music-as-written) is art.
Even the sheet music might be art, especially if it's handwritten and illuminated.
I agree with you [VandenBerghe] that gameplay, especially where exceptional skill and or insight are freely at work, can be art. (And thank you for reinstating it as also expressive; it's a hugely important, and neglected, point.) But that doesn't mean nothing else in the equation is.
We don't have the language to describe the poetry of system yet, and we're not conscious enough of it as a form of poetry. [Poetry here is used in the way justice can be "poetic"; it comes from from the Ancient Greek for "making" and means anything artfully made.] It's a chicken-and-egg situation; until we start talking about it in these terms (to see what makes sense as much as anything else) we can't think about it in these terms, and vice versa.
But let's be clear. If a movie is a more or less artistic arrangement of more or less meaningful images and sounds (and optionally but usually plot, character, narrative) - a game is a more or less artistic arrangement of more or less meaningful judgments and decisions and tests-of-skill and random inputs and consequences of all the above, possibly with one person playing it, and possibly as a meeting ground for more than one.
The point is:
although the elements being arranged are different, experienced differently, and appreciated fully only over a longer timescale and possibly in the context of multiple plays of the game,
the basic act is the creative act of arranging meaningful elements to produce an experience or sensation, and/or to express an emotion or idea,
and the basic act is therefore is fundamentally the same in designing and playing games as it is in composing or playing music, or any other artform.
Gameplay can be artful, and whether intended that way can certainly always be judged on that spectrum. Game design - or should we call it game composition? - is always artful. It may be crass art that deals with its subject matter only in the most superficial terms, and I would argue a great many games are; but so is a lot of music and a lot of cinema, and that doesn't disqualify them from being art. They're not great art, or what Moriarty calls capital-A "Art"; but they're still art in exactly the same way movies are, and Ebert's lack of systems literacy (while hardly blameworthy given the wider cultural context) doesn't change that at all.
And therefore I'm with Moriarty:
games are art, but really, pretty much anything can be, so who cares about this?;
and games CAN be Art, and not enough are;
and (my corollary) we need to get better at talking about the unique forms of poetry offered by our medium as such, so we can get to the games that are truly, life-changingly great - and maybe even some that tell truths only games can.