Video Games As Art

[Laddy]

I'm writing a paper arguing for the status of video games as an art form, and what I need are specific examples that support my case. So, in your opinion, what games hold the most objective artistic merit and why?

Some games I am writing on:
Alpha Centauri
Silent Hill 2
Spec Ops: The Line
Shadow of the Colossus/Ico
Planescape: Torment
Portal

EDIT: I want to avoid so-called "art games" as I find them generally lacking in narrative, auteur theory, and direction, all areas that I feel my examples best support.

EDIT2: Forgot Okami.