There were complaints about Super Paper Mario and it's 2D/3D gimmick. You can only do it while playing Mario, and the other dimension was pretty boring. Kokoromi studio in Montreal has done it up right:

Not only does the flipping dimensions go a full 360° but each 2D view is interesting and playable. I hope this finds its way onto the Wii, DS, PSP, or PS3, I don't want to have to buy an XBox 360 just for this...