As far as uniqueness goes, I'm going to give the areas a 10/10 rating. I noticed while playing Skyward Sword that Zelda has never seen the style that the provinces were designed to be (at least in 3D). Nintendo promised that each area was going to be very different from what we've played through before, and they were right on that. The entire Surface looked like a huge puzzle, filled with varying levels of
high or low grounds rather than the typical
flat but vast overworlds. This brought on entirely new challenges of ways to reach different area or find a desired target (such as a Kikwi or Piece of Heart).
The biggest similarity I noticed is the log rolling in the Faron Province. It was previously used in Wind Waker, during the sequence of going through that obstacle course before meeting up with Tetra for the first time. Even though it's a very short scene and takes five minutes, it's the most comparable incident I can come up with. Which means that Skyward Sword's overworld is indeed rife in its diversity.