1 - What is art?
I don't mean to be a stick in the mud, but this is a fruitless discussion. There are as many answers to this question as there are works of art.
As for my personal take on games as art: First and foremost you should concentrate on games as games. A game should be fun. Any art, message, or feeling you want to convey comes second. It's a limitation of the medium. Just as you can't sculpt with watercolors, and you can't paint with marble. If you make a game that's not fun, or isn't really a game (i.e., it's just an "interactive experience"), then you've failed at making a game, and any message you intend runs the risk of being lost.
I think the idea of games as art is nice, but in reality I've never seen any gameplay mechanic that was integral to delivering the artistic message. Yes, I thought Shadow of the Colossus was moving, but it was the imagery, the music, and most of all the story that moved me. But those are simply art elements that are incorporated into the game. They are secondary characteristics of the game as a whole (or, if you like, the game is a secondary characteristic to the story). The gameplay itself was similar to many other games that I've played, but I had no such reaction to those games.
So, can a game be art? As a whole, yes. But unless you are terribly clever, a game mechanic on it's own isn't likely to be art. If you were to remove the music, imagery, and story from SotC and recreate the gameplay with simple colored blocks it would lose all meaning, or at the very least take on a different meaning. Games are dependent on other forms of art to make them art. Games are the canvas on which you create your art, not the art itself.
Also, on an unrelated note, you seem to suffer from "wrong-forum-itis." This thread belongs in Open Topic, and your other thread belongs in Help/Tech . Just sayin'.