In the PC series, I think tha Syberia is one of the most artistic games. The Nancy Drew mystery collections and Syberia is one of my favorites to play.
Okami definitely, its the most beautiful, imaginative, just all-out amazing adventure. Everything is so stunning in the game, from the white wolf Okami, to the tiniest leaf in your surroundings, the levels are masterful in design, I just love that game so much, a true Japanese masterpiece and you really experience the Mythology of Japan. omg I must play it again!
Another legendary game is Shadow of the Colossus, jaw-dropping
Passage by Jason Rohrer
Cloud, Flow, and Flower by That Game Company
I Wish I Were the Moon, and Today I Die by Ludomancy
Pathways by Terry Cavanagh
Some games that some people might consider artistic
Braid, Cave Story, 4 Minutes and 33 Seconds of Uniqueness, Indigo Prophecy, Robot Alchemic Drive...
I'm surprised barely anyone mentioned Killer 7, which I think is probably the uber artistic commercial game out there.
Okama was pretty good, but I've got to say pong was FASCINATING for the people that saw the first video game. What is it like 5 pixels? 1 for the ball 2 each for the paddles, amazing.