Trilarion: Games are art but art doesn't mean much. Often art in games is very low quality. Like in a tuppenny novel. Although there are exceptions.
It's not so much that the quality of video games as art is low quality, but rather that the potential of video gaming to create art is not used in the mainstream to its fullest extent. Most mainstream titles seem to want to imitate film and introduce an interactive element.
It's when games abandon traditional film concepts like linearity, (so many so-called "open world" games, like GTA, are still linear in the round) pre-defined outcomes (as opposed to emergent gameplay) and fixed dialogue that the idea of gaming as art comes into its own.
I consider Minecraft, for example, to be a piece of art that cannot be reflected in any other medium. It makes statements on human survival and the development of the built environment in a way that no linear narrative could, not least in the way it organically makes statements about resource exploitation.
Braid is another example, whereby this kind of perception of time simply cannot be reflected in a linear narrative.
Another is Bastion, which enables the player to influence the narrator which his actions.
Edit: keeveek also mentioned a couple of excellent ones up there.
Games require the beholder to experience the consequences in a given situation resulting from their own actions, and linear games just cannot achieve this. If I play Call of Duty, failing to keep to the established narrative simply ends the game or forces limits upon me. Even Skyrim, the much-acclaimed bastion of freedom, doesn't fare much better in this regard, because the storyline threads are always set, no matter which order you play them in.