Here's what I expect from the ocean levels:
1. Considering that PU will take on an island, I expect the beaches to be fun, and also playable, like Super Mario Sunshine's Gelato Beach, or Sirena Beach w/the hotel.
2. If we're talking about swimming levels, I expect something like The Legend Of Zelda: Majora's Mask 3D when link puts on the dead Zora's mask, and goes on a swimming quest, or the swimming levels of, get this, Ty The Tasmanian Tiger, if anyone at all remembers.
3. If we're talking about boats, then I really hope it wouldn't be boring just like The Legend Of Zelda: Wind Waker, in which you would spent countless of boring-a** hours just to try and find that special treasure chest that doesn't even appear on the freaking map!
That's what I'm expecting.