One "rule" I think it's useful to keep in mind (not deadly seriously, more like an interesting idea to play with) is to look at Freud's pleasure principle.
Freud's pleasure principle basically suggests that the fundamental drive of the id (the disorganized, animalistic part of the human psyche) is to seek pleasure and avoid pain. This manifests in a constant desire for immediate gratification. When you're hungry you want to eat, when you're thirsty you want to drink, when you're horny you want to be sexually stimulated, when you're frightened you want to escape and be comforted. This is the basic motivator of human activity and the source of any kind of compulsive behaviour. If you watch how young children behave when they want things or don't want to do things, you'll see the pleasure principle at work.
As people grow up, theoretically, they stop being wholly governed by the pleasure principle, they learn how to subordinate their desire for pleasure to the needs of reality. They learn that they can't just eat ice cream all day, they learn that they can't masturbate in public (unless they start a viral campaign to raise awareness of an African warlord first).
I think this primarily why modern porn is not generally considered art, because porn is shot completely in line with the pleasure principle. There's no boring story, there's no context or relationship between characters, there's no deferral, there's no sense of realism or if there is it's pathetically transparent. You put on a porn movie, and you're being presented with a fantasy where the entire point is to stimulate you pretty much from the moment you turn it on. It just exists to fulfil a basic pleasure drive. It's no more art than a nice steak dinner is art. Sure, it's an experience and it's enjoyable, but that's not what art is.
So basically, I think the key question is this. Are video games toys? Do they exist simply to stimulate people in a way which they find pleasurable and uncomplicated? Are they just hotwiring our brains by providing pleasurable stimulation, or are they actually doing something more sophisticated? I think video games are still more like toys than most art forms, which is why people become compulsive about them in ways most people don't with movies or books, but I think there are many, many games now which could be considered to go so far beyond basic stimulation. In fact, I think you'd be much harder pressed to find games which are just an endless torrent of stimulation, because at the end of the day successful video games now have to appeal to adults, and most adults get bored of that.
It'd be interesting to think about where really compulsive games like MMOs fall on this scale though, and I think that's where the principle breaks down. MMOs are full of deferral, but also massively compulsive and habit-forming. In fact, the deferral is part of why they're so addictive, people play for hours just to hear the 'ding'.
To explain why people get so hooked on watching numbers slowly increase, even when they're barely paying attention to any semblance of story or context to their actions, I think you need to move on to ideas about conditioned responses which have unique significance to video games. It's very hard to condition a response within a single film. Over our lives we learn how cinematic language works and thus how we should feel at particular clichéd moments (ooh, happy music, this scene must be funny!) but ultimately a director probably can't condition a response within the space of a single film. It's incredibly easy for a video game to condition you to derive pleasure from achieving a completely arbitrary reward, and I think that genuinely does open up genuinely new questions about where the line is between something which is art and something which is just stimulation.
But yeah, I think most games now probably qualify as art. What else would they be? Toys? Porn? Random stimulation?
Sorry, I've been over-thinking this one for a while.
