Wind Waker's overworld was a mostly empty ocean. Basically was the first step in Nintendo's effort to cut that component out of Zelda releases.
Even when you realize that the main hub of Ocarina was similarly empty, the interesting overworld bits spread throughout all 4 edges of the map (And the ranch that was right in the middle of the hub) still far outnumbered the amount of areas to explore in Wind Waker.
Give me lots of land, villages, cities, castles, forest, bays, mountains, harbors, deserts, and so on to explore. And plenty of task to do in those areas in between dungeons (And not just fetch quest and collectathons).
If there's anything I want to see change in Zelda, it's the overworld. Gameplay is fine and dungeons are fine (Although there's not enough of them anymore compared to Link to the Past and Ocarina of Time). But I want an overworld that couldn't fit into one of the Imperial City's districts in Oblivion with room left to spare (Not that I'm suggesting they copy Elder Scrolls; I want traditional Zelda, just with a bit more substantial overworld).
Basically, give me enough content where they don't have to lower themselves to artificially extending the length of the game through things like the Triforce hunt in Wind Waker, the repeating dungeon in Phantom Hourglass, and so on to pad the game to reach the length they desire.