There are 3 parts to any communication:
the sender’s intended message → the medium → the receiver’s interpretation.
For a mere transfer of information to become art, there is a conditional attached to each link in this chain:
Intent: Does the sender want to generate an emotional response(s) in the receiver?
Medium: Is the message well-delivered (is the finished product indicative of skill, talent, and dedication)?
Interpretation: Does the audience experience the intended emotional response(s) when participating in the art?
If the answer to any of these questions is “No”, then it’s not art.
But the reason art is subjective is because of one extra question: does the audience believe that the work satisfied these 3 conditions?
Poker isn’t art, because nobody put a meaning in it for us to experience. That doesn’t mean you can’t get an emotional response from Poker…but it isn’t art. Same with a beautiful sunset. A piece of tragic news from a neutral third party isn’t art, even though it has meaning and causes an emotional response, because the implementation is mundane. There is nothing to say, “It took skill to craft this product, and to cause you to feel what I wanted you to feel.”
"Schindler’s List" is art, because the creator wanted us to be devastated by the message, skillfully delivered it, and caused the intended emotional response.
“Showgirls” is not art, because nobody believes that the creator's intent was to say “look at how skillfully I can make a movie appear to be unintentionally hilarious!”
Sometimes there is a greater focus on the technical execution of the art than on the information content of the message. The drawback is that the less expertise an audience-member has with an artistic medium, the less he can appreciate the skill involved in its creation. Conversely, an expert experiences more from a piece of art than the layperson; I don't get anything out of Bach, but I love a great game design - my father is the opposite.
(Here comes a tangent, but I'll return to the previous point at the conclusion.)
Can a slam dunk in basketball be art? Yes: when Michael Jordan could very easily put the ball in the net with a lay-up, but instead chooses to perform an acrobatic and difficult dunk, then he is saying, “Look at how skillfully I can do this,” intending to cause awe in the audience, and succeeding. However, when Michael Jordan routinely hits a shot during warm-ups, there's no message, and nobody believes it is art.
I think that people commonly believe that games aren’t art because the sender's message isn't fully formed when it is placed into the medium - that there's nothing without the receiver's participation. Nonsense. Art doesn't exist until the audience experiences the sender's message and believes that it achieved its purpose:
From this perspective, the only thing that separates a painting from a performance from a game is the degree to which the final form of the media (which itself is only one-third of the equation) is determined by the artist.
Now, given the above, which is more impressive: a book with an emotional impact (where the sender had total control over the medium), or a game with the same?
Remember when I said I would return to the following point?
the less expertise an audience-member has with an artistic medium, the less he can appreciate the skill involved in its creation.
If you don't think games are art, let me ask you this: how much expertise do you have as a game designer?
Circular logic, perhaps, but if you were able to detect it, than you agreed with me long before now, didn't you? :)