Originally Posted by Monolith

I get what you're saying. One analogy could be a piece of paper. Gameplay would take place on the surface of the paper, but the paper itself could be bent and curved. I like that idea because it keeps the gameplay simplified to 2D, but the environment can still be enhanced with 3D technology. One example that comes to mind is Ikaruga. All the gameplay is 2D, but the camera follows a curving path through a 3D environment.