Metroid: Other M.
I say that as a soon to be M.A. in literature. The plot is complex, but still easy to get, the narrative elements are well done, and the flashbacks, although sometimes long, all add to the current state of mind of Samus. From a feminist perspective, the game is great in showing Samus as a strong female protagonist that becomes strong on her own terms rather than the patriarchy's terms, and that keeps her identity.
You want more? Without going in the whole post modern view of culture, I have to ask this: what is a valid art form?
If you take painting, isn't anything on the canvas representative of a valid art form? Does a painting require a certain level of "greatness" to be seen as art?
In fact, what is art? Can you answer this?
Games that are entertaining and aesthetically pleasing are art. Hell, they don't even have to be pleasing. Many people don't like cubism, or Picassos, or modern art, but they would be hard pressed to say that it isn't art. So what is your justification to claiming that Nintendo's games are less artistic than another company?
(Also, in 2000, so in the last decade, Nintendo released a little diddy known as Majora's Mask. Even if you ignore the fact that you cannot claim clearly what is or isn't art, you have to realize that Majora's Mask is a very artistic endeavor.)