I agree that they are art for the reasons that you stated too. You experience what they created and depending on how they want to turn it, the ending could make you sad or extremely happy. A painting could have that affect on you as well.
I know that when i play a game and the game ends with a sad ending then the credits roll with beautiful music as you see the characters and scenes throughout the game in the background.... I start to tear up. KH 2 and KH 365/2 days did that to me.
Videogames are art. They portray it through the story, the feel, the music, the art style, and the characters.