Just to add a few things to my above post:
I agree with Roger Ebert.
Bang. Contentious, yes? Ebert said that art requires authorial control, and that player agency allowed in video games negated this, and as such...no art. Ebert is wrong, but not, I think, in his main jist. I too belive that art needs authorial control. Games, of course, do have authorial control. Player freedom is an illusion.
You may think that you entered that room and decided to go and pick up that wrench, all on your own free will, but truth is that good designers would have used expert positioning as well audio and visual cues to lead you to that wrench.
In multiplayer this is simply much more difficult to do. I guess you might have the odd moment in multiplayer where something strikes you and makes you think, but these would be few and far between, and happen by sheer coincidence. If competetive multiplayer is art, it's only very rarely, and by sheer chance, in the way that would shrivel when compared to authorial art.
Hmmm....this topic has made me think quite a bit. In the end though 'art' is subjective, and there's no real answer. The above posts are simply my own interpretations.