And by this I mean a game that is multiple dimension and reality spanning. I was thinking about it a lot when playing The Legend of Zelda: Twilight Princess and thought it'd be really neat to see a Legend of Zelda game in which all of the different previous Legend of Zelda games tie into as a sort of "hub" of that series. Since that series constantly retells the same story of Link vs Ganondorf it'd be interesting to see the many Links and many Ganondorfs that have been created come together.
Then I got more into thinking about how it would be an awesome computer RPG that breaches multiple fantasy worlds. There could be a traditional medieval swords and sorcery fantasy world, a modern lovecraftian horror world, a science fiction fantasy world, and who knows what else. It would be the most insane game ever. Your party could end up with an elven fighter, a cowboy, a Navy SEAL, and a space marine all standing on a castle wall fighting off space aliens sent by a demon or dark god! All the while the town folk are just freaking out. And of course, at some point pirates and ninjas would appear.