I had to rewrite the first and last paragraphs because my mom closed the reply window while I was gone (for the first paragraph), and the page froze when I clicked on the image button for the last paragraph, so I apologize in advance if these two paragraph look somewhat sloppy.
There are quite a few things that Nintendo could do to mangle the Skyward Sword experience. The first of these is the visuals. Before Skyward Sword's E3 2010 Trailer, I was greatly anticipating any news or footage of the game, hoping that it would be more like Twilight Princess (except with a much higher difficulty). My ideal Zelda game at the time was a game much like Ocarina of Time or Twilight Princess, one with realistic visuals, beautiful scenery, the classic Zelda feel, and an epic final boss battle that would far exceed those of OoT and TP in terms of grandeur. Taking a single look at Skyward Sword told me that it wasn't going to be that sort of game.
I remember first viewing the E3 2010 Trailer like it was yesterday, and I remember even more clearly how my heart sank when Link made his appearance, clutching his sword while it was still sheathed. I was severely disappointed by the visual blend of Wind Waker's cel-shading and Twilight Princess' realism. I love both those games and their graphics immensely, but I was really expecting something much more ambitious from Nintendo. I was really expecting Nintendo to craft a game with visuals with as much detail as XBOX 360 and PS3 games. Seeing the improvement from the Wind Waker to Twilight Princess, I assumed that the next Zelda game would have a graphics engine that's nearly as powerful as those of the games on other current generation consoles. I was wrong about this, but I've come to appreciate Skyward Sword's visuals. My "pretty Zelda game" dilemma disappeared with the announcement of a revamped and refined Twilight Princess with the Wii U, so I really have no problems with SS' cel-shaded graphics. That last statement is especially true since Nintendo decided to turn SS' brightness down a shade to make the game "darker".
Instead, my concern is mainly for the art direction that Nintendo may take for enemy design. Enemies and characters I've seen so far have been rather cutesy and harmless looking, much like those from the Wind Waker. However, I love the Wind Waker's visual style, but I really do prefer more realistic characters and enemies. This doesn't really detract too much from the game, but hopefully Nintendo will decide to place some more threatening and realistic enemies in the game to make the game seem less childish.
Another issue that could arise in Skyward Sword is easy difficulty. Wind Waker and Twilight Princess, the two most recent home console Zeldas, have both been cakewalks. Nintendo shouldn't be so foolish as to make such a mistake again (especially when they claim Skyward Sword will be the best Zelda so far, or else they'll stop the franchise). The fact that Nintendo would say such a thing somewhat restores my hope for the game's difficulty, and if they've been listening to their fans, they'll comply.
One last thing is this: Ghirahim can't be a wimp like Zant was. Sure, Zant was an intriguing character, but didn't completely fulfill the role as TP's most menacing villain. Ghirahim honestly doesn't look so fierce, he looks rather like the opposite. What made past Zelda games so epic and magical were the villains. If it weren't for Ganondorf, Twilight Princess would've been a lot less impressive (though Ganondorf was not sewn so well into the story). Some critics that have played Skyward Sword in advance have commented on Ghirahim, calling him an interesting character with a unique boss battle that is unlike any other in the Zelda franchise. I sincerely hope that Ghirahim's boss battle and the entirety of Skyward Sword will have an exciting atmosphere and feel epic. Honestly, I expect Skyward Sword to be almost (or somewhat) as legendary and heroic as Ocarina of Time felt, or else I would consider the game's feel to be below my expactations.