Yeah, sure 3D Land and 3D World do have three-dimensional gameplay, but in every other aspect they feel much more like the 2D side-scroller Mario games.
Seems like a lot of people would have wanted more direct sequels to the already existing 3D Mario games. I'm not against that idea myself. Galaxy 2 has already proved to us just how well Nintendo can make a second 3D Mario game using very similar mechanics at the previous one. In my opinion...