I don't really care about voice acting ... More side quests would be nice and increasing independent exploration would be a plus but are not essential.
With that said, I think the primary thing Nintendo has to do with the next Zelda is start to break away from the Zelda formula to some extent. The story, world design, dungeons, boss battles, collecting, puzzles and many other elements of Zelda games are very closely related from game to game and for the series to improve Nintendo has to break with this formula.
What I mean by this is (to a certain extent) what Nintendo has done with 3D Mario games since the N64. While there are obvious similarities between Mario 64, Super Mario Sunshine, and Mario Galaxy a large portion of the gameplay mechanics has changed dramatically making each game play very differently. In contrast, Ocarina of Time, Majora's Mask, Wind Waker, Twilight Princess and Skyward Sword all have unique elements but (in my opinion) each version plays far too closely to the previous game; and as a result it is less interesting/exciting to play.







