There is Therefore a Strange Land is a multiverse game. Yes, that's right. Multiverses. It's not your father's multiverse, by any means (I'll post a proper 'manifesto' at some point soon) but it is about PCs adventuring in, er, Strange Lands. To what end?
Well, the main reason is because the Muse took me. And when the Muse takes me, I go with her. (My Muse looks like Kelly Brook; I don't know about yours.) But there are other reasons.
First, I love Planescape, but - to return to a Monsters & Manuals favourite from yesteryear - it does have the tendency towards banalifying the fantastical. It does a wonderful job of making you want to run games in its vision of the planes (there has never been more packed into an official D&D setting, by a long, long distance), but it also reduces them, in a sense, to just another fantasy world. It tames a lot of the mystery. I think this in part because of a strategic error: making planar PCs an option, and making Sigil with its factions the centre of everything. It instantly deprives the planes of a sense of wonder if you domesticate the whole affair by making it something the PCs are familiar with and engaged in from the outset; The Hobbit may have been perfectly good if Thorin and Gandalf had been the main characters, but it wouldn't be the anything like the feeling of adventure you get with the perspective being Bilbo's.
Second, other attempts at interdimensional or cross-dimensional games tend to leave me cold through being obsessed with themes. The most recent example of this sort of setting is that found in The Strange. I've absolutely nothing against it, but it simply doesn't engage me in the slightest. These things are a matter of taste, of course, but everything I've read about it makes it sound like "Sliders: The RPG", and I don't want to play "Sliders: The RPG". I don't want a multiverse setting to be "Let's go to Wild West Land this week. Next time it's Bizarro World, and after that Everything Is Dinosaurs". It's all a bit too much like The Magic Faraway Tree for my liking.
So I feel like it's about time multiverses got the noisms treatment; if only to try to prove that nobody has even tapped that well properly yet. And if you don't like it, you can break it to Kelly.