Personally, I think all video games are art. But in general, they're all just video games.
If your going to make any visuals in a game, whether its a enemy made of red pixels, a weapon made by polygons and metal textures, or a cutscene/FMV using live actors, you need art to bring it across and make it represent what you want it to. But you don't just call games 'a work of art' in the same way you don't call games 'a work of engineering/coding/acting/literacy/production.'
If someone want to make a game because they have an artistic vision or story, then fine. It's 'art', but it doesn't necessarily make it good art. Super Mario wasn't made to be art (FACT: Mario was given a mustache because it was easier than animating a mouth), but the art it contains does it's job well. It's simple and creative, sacrificing detail for clarity, The pixelated art of Mario is now the symbol of a leading game company, as well as a symbol of gaming in general.