I think it'd be fun to have a 3D game with the explained 2D navigation mechanics... Looks like classic Mario Bros, until you shift... Add in some 3D baddies and a 3D observer mode, where you can see everything while "watching" players in the game.
FWIW, there is a 2d in a 3d world side scroller called Fez
It's way more limited, you can only rotate to 4 faces around the world. It's been a decade, but I remember it being a fun and short game.