I know there's a difference of opinions here, but I really liked the style of Wind Waker. Sure, there were a few issues (sailing, short game) but it brought more memories of Link to the Past than any other console Zelda game since then. I hope that Wind Waker doesn't lend itself to only be used on the hand held.
As far as ideas of what should be in the next Zelda...
Exploring - Sure, Zelda has been somewhat linear to an extent, i.e. kill this boss, proceed to next dungeon. But I felt Twilight Princess was way too linear and there was almost little to no reward for exploring. With previous Zelda games there were tons of caves and dungeons that were by no means required to visit, but were there for the curious explorer. There was not enough hidden secrets to find in Twilight Princess, and I pretty much obtained everything on the first play through.
Difficulty - Maybe it was because I was a kid and it seems harder now, but I'm looking for the next Zelda to take a step up in difficulty. I don't want to be able to easily obtain everything upon the first play through, I want to be stumped when I reach certain puzzles. A lot of difficulty seems to have been lost in the translation from 2D to 3D. I realize they may want to try to push Zelda out to more masses, but I think that would almost ruin the essence that is Zelda.
Minigames - Okay, so maybe I'm a sucker for games in Zelda but that was one of the few things I liked about Majora's Mask. There were plenty of other things to do when you weren't saving Hyrule. Every hero needs a break now and then.
I think whatever team is working on it needs to sit down and consider, what is the essence of Zelda? What makes a Zelda game, Zelda? I suppose the most difficult thing is giving the series of fresh air that it needs while still keeping it "Zelda". That's no easy task.
Oh and delays. Please don't announce it until you're sure you're ready to announce it. I hate hearing "bla bla in 2008" only to be released 2 years later.