Fez just hit the App Store yesterday, and I've been having a blast with it all day today.
Considered a modern platforming game classic, and the primary subject of the critically-acclaimed film Indie Game: The Movie (93% on Rotten Tomatoes!). Fez presents itself as a classic 2D pixel-art platformer, but quickly changes things up by introducing a novel new 3D perspective shifting mechanic.
Using the shoulder buttons, you can shift the camera between 4 views, revealing new perspectives on the 2D platforming world you inhabit. Changing the camera perspective flattens every axis back into two dimensions. As a result, platforms that would be far away along a Z axis in a three-dimensional world can be brought right next to each another when flattening back to just the XY axi.
This is a difficult mechanic to describe, but it quickly becomes second-nature during gameplay, and is a novel, unique take on bridging three dimensional and two dimensional platforming games.
I know this one is a hard sell in writing, but if you're a platforming game fan, you need to take my word on this one - there's a reason Fez has gotten as much acclaim as it has. It may look like a bunch of other indie games, but Fez is one of the most important games to hit the App Store.