I think the "dream" atmosphere is very hard to get right in games; it's much easier to do in stories which aren't interactive.  (Perhaps this is because when you are awake enough to consciously test a dream and interact with it, you're likely to wake up, but when you're passive,  the dream lasts longer.)

What I call "Surrealism" can be found from time to time, but art scholars will probably tell me I'm abusing the terminology.

A not-very-surreal set of illustrations is at this link:
http://www.alisoncarey.com/OrganicRemains.html

While the above are not very good, they might serve as mood-settings for RPGs.

A rather surreal and pretty set of illustrations follows:
http://www.boredstop.com/liquidfire.htm

The second set has a simple theme: "What would it look like if fire were made of water?"  It is concerned with the appearance, not the essence.  It does not concern itself with consequences.

Hard-core "what-if" analysis brings two disparate areas to my mind: business analysis and science fiction.  Both of these disciplines ask "what if?" but one of them purports to be sober, productive, and billable, whereas the other sells itself as a flight of fancy.  Both of them are more concerned with the essence rather than the appearance.  Both of them tend to center on consequences.

Pirsig wrote eloquently about the romantic/classic distinction, dealing with appearances and essences.  Using this distinction to examine dreams, I claim that dreams can remarkable on both counts.  Dreams can have remarkable images, and dreams can have remarkable meanings.  Further, one can take an image inspired by a mundane meaning and use it to allegorize a more remarkable meaning.

I think fantasy  games are analogous to dreams.  They can be cliche, they can be inspired, they can lean towards appearance or toward essence.  But most of all, they are recombinable and modifiable, so that their images can be used for meaningful statements.

I have only seen game behaviors that are meaningful on a personal level; interestingly, player choices seem to be on an equal footing with referee plotlines.  I've seen a lot of players make choices that resonate perfectly both with the game and with the long-term choices of that player in real life.

So, just as a dream can cause a person to wake up and say, "Now I realize what has been bothering me for so long and I know what I should do," a game can cause a gamer to say, "Because I had fun with an element that was cool in the game, I realize now that I believe something real about the real world."

This kind of epiphany doesn't always happen.  Certainly it's not what most gamers are looking for, when they sit down to have fun with dice, maps, and buddies.  But I suspect it is a large part of what keeps people coming back to various forms of art, various forms of games, and various other forms of fantasy.