So, I occasionally like to write what are, for lack of a better word, essays on subjects that I am passionate about. Games as something other than just a childish way to waste time is just such a subject.
On the escapist forums there is currently a thread on this very subject, referencing a link that lists 10 such games. The list primarily mentions audio and visual aspects, and thus many posters are arguing that the list is therefore invalid. Admittedly, the list may be flawed, but that does not mean it is invalid. Some claim that art is subjective, and in a way they are correct, but isn't that less that something isn't art and more than you do not like that particular example of it?
I hate most modern art, but that does not mean it is not art.
I think, to describe art in the most objective way possible, it must use the medium in a way that is unique to the medium.
That does not mean art has to be "original" or that it has to be the first to use the medium in this way (obviously, more than the first painting can be a work of art)
All mediums are limited, some more so than others. Pictures on canvas can never encompass sound, and music itself cannot encompass pictures (though, album art or music videos can combine the two.)
So, what do games have that is unique? Interactivity is the most obvious, but something would have to have a truly revolutionary way of having you interact with the game in order to qualify, surely? Can the Katamari games count purely because of how you interact with the game world? Possibly.
But now we have hit upon a key term - "game world" though a visually appealing world by itself is probably not enough. The Lord of the Rings films are not art purely because the castles are so impressive (plus, what is impressive varies with time, and "visually appealing" is far too subjective a term.)
So what else can there be in terms of game worlds? The most obvious thing that springs to mind is level design, but how can that constitute art?
Games have many aspects to them: Gameplay, Interaction, Controls, Game worlds, Level design, Story, Music...
Most of these can be linked together, but the toughest to link fully into the set is story. Story can be partially told through music, but how can you tell the story through the other methods?
Psychonauts provided perhaps the best example of such an attempt. Many other games will have the story told using objects within the game world, like a phone, or a poster, or a diary.
Psychonauts could tell it through the design of the level. Not to say that it could describe the plot, per se, but that it greatly contributed to the characterisation (which is an integral part of the story but not the story itself.)
Throughout the game you had levels taking place in the real world, and levels taking place within the minds of others. These levels were representations of the personality of the characters, and also within these levels you could find safes containing hidden memories. These memories were sets of pictures, never more than 6 of them, which added a lot of characterisation.
The levels described how the characters are at that point in time, but the hidden memories described why they are that way.
The Milkman Conspiracy is a particular level which is often used to try and demonstrate this, but to choose only a single level to demonstrate the point doesn't quite demonstrate it enough, in my opinion. All of the levels, without exception, have this wonderful feature.
So, why does this feature constitute art? Because it is using the medium of computer games in a way that is unique to it - a series of pictures of the level and the memories could not have this effect, nor could mere words do it quite as effectively. Video games are a combination of music, complex visuals, story, dialogue, and interaction. None of these by themselves is effective, but it is the combination of all of them. Why did I include interactivity in that list? Because the location of the memories is important - they are hidden, after all.