To me, 3D Land is the ur-Mario. They had to take all this time finding what 3D Mario really is, getting the formula wrong with Mario 64 and slowly righting it, taking their time so as not to make a big misstep. With 3DLand, they arrived at the basis of what 3D Mario is, what Mario should be when you add an extra dimension. They couldn't focus on the innovative designs of Galaxy 2 because they were working so hard to redefine the core concept. And they finally did it, and now we're going to get the best of both worlds. When some people look at 3DLand compared to Galaxy 2, they're seeing a lack of ideas, a step back, something on a smaller scale. That small scale is because of the platform, the lack of unique ideas for every level is a because they tried so hard at redefining the series.
I could be wrong, but I think people are going to be really surprised when they play 3DWorld, because I think it'll be the best of both worlds, the forward-thinking level design and scope of Galaxy with the pitch-perfect gameplay and Mario feel of 3DLand. The reason it looks like 3DLand is because it falls under the paradigm-shift. It's not the old, un-Mario 3D style that felt like such an awkward transition. It's a primal representation of what the series is about, pushed ahead with everything the team has learned about level design. When people say they love Galaxy 2 the most, they're saying they love the per-level ideas. Galaxy's level design really has nothing in common with 64 or Sunshine, it's just held back by their control and systems design.
I think there's a lot of merit to revisiting 64's exploration-based gameplay now that Nintendo's gotten the framework down, now that they've figured out the 3D space more, now that they're better able to guide players. But I definitely feel like this game was in them, that it was incubating for a long time, that they finally realized their design goals with 3DLand and they're bursting to try them all out, to create a four-player playground bursting with new ideas and level designs.