Given that the game tried to expand itself in terms of landscape, I personally thought it failed because not only was the land barren or "empty" (especially the sky), but I thought there was nothing that was truly inviting to make you go explore. Like no hidden paths, secrets, caves, etc. Granted Zelda has never had a surplus in that, but I thought SS lacked way more than others.
With the next Zelda expected to be on Wii U, I hope they take a page from some of the top quality sandbox games such as Dark/Demon's Souls or Assassin's Creed in creating an environment that can be both lively yet inviting to explore. For example, if you're in town, it'd be nice to have the bustling streets, while you can still talk to key NPCs and what not. When you're exploring the forest, perhaps a shortcut, alternate route, or maybe altogether a path that leads to another part of the game.
Castle Town in TP was pretty awesome in that regard, they should bring that back. Skyloft felt so dead to me.
The one thing that would make Zelda super awesome is the one thing that will never happen: more options for Link. One of the reasons that those other games work so well is that you can get great items for straying off the main path. In Zelda though, it's THE MASTER SWORD. THE END. Even if there were optional dungeons and secret caves, all we're getting is heart pieces and rupees for the effort (MM has been the best exception to this, with the rewards actually being pretty awesome). At this point, I'm not even sure they could add items to be found outside of the main dungeon. SS completely gutted the item system in Zelda to place the focus on sword combat, so that most items just became puzzle tools instead of weapons. There'd have to be a big step back from swordplay to make the other items combat relevant.
I'm really starting to dislike Zelda lore, because it curtails so many options in game design. I think what's holding Zelda back is Zelda itself: its unrelenting adherence to the story of the franchise. I mean, all right "The Sword of Evil's Bane" or whatever, but in the modern gaming world where technology makes so much more possible, it's kind of absurd that we're trudging along with pretty much the exact same sword the entire game. Why shouldn't Link be fully customizable, with different weapons, equipment and costumes? Upgradeable armor, weapons, maybe even a spell casting/magic system where Link learns spells? I thought the whole point of Link being a silent protagonist was for him to be an extension of the player. And not the lame upgrade system in SS, a deep upgrade system with branching options where actual cost/benefit analysis can happen. There was no reason NOT to upgrade your beetle or bow in SS, and the upgrade options were linear and severely limited, so it felt more like a chore to gather all that stuff than an opportunity. The differences between shields was a good initial step in offering choices between equipment, but even that was negated by the holy shields.
The focus on "The Hero" (which didn't exist before OoT) has really stunted the possibilities in the Zelda franchise. Now, to be Link, you must have the Master Sword, the Hero's Tunic, and the Hero's shield. I'd gladly give up all the lore if we could get some variety in future Zeldas. I'm not saying turn the game into The Elder Scrolls: Hyrule, but it seems like Nintendo doesn't even consider other possibilities for Zelda games.