What's Your Favorite Kirby Ability?

[Kriven]

When speaking in terms of platformers, 3D and 2D refer to the play area, not the graphics. 2D platformers exist on two-dimensional playing space... left, right, up, down. 3D platformers exist on a three-dimensional playing space... left, right, up, down, near, far. It's possible to create 3D gameplay with 2D assets (Doom, Paper Mario) or a 2D game with 3D assets (Kirby 64, Klonoa, New Super Mario Bros., Yoshi's Story) although this isn't traditionally done. Examples of 3D platformers: Banjo-Kazooie, Super Mario 64, Croc.

I'm not understanding your argument about movement at all really. NSMB allows you to move left, right, up and down... It doesn't allow you to move toward the background or foreground elements at all. You can't run in circles, only back and forth... just like Kirby 64.