I really hope they stay true to the original artstyle, while making the obvious enhancements. I'd hate to see them change too much and completely ruin the tone of the game. So on the visual side, more subtle effects than anything else. Keep the darker colour scheme, but make the textures nicer to look at so to say (just more detail really). Then throw in more vibrant colours in the lighter sections of the game - Lake Hylia, Castle Town, Gerudo Desert etc. - to create a real contrast between light and dark, which is what the game's based around anyway. Then I'd like an enchantment to the character animations, so facial expressions and the like.
This also kind of relates to visuals, but add in dynamic whether and lighting effects. The game tried to do this somewhat, but we're talking 2006 technology and hell it looked amazing at the time, but now we're essentially two gens ahead. So I'd like to see the light of the sun really effect the world; how it comes through the leaves in the woods, how it reflects of the water in the lakes etc. Then make weather more dynamic. We saw heavy rainfall in Hyrule Castle, So why not build upon this concept in the entire world? Have thunderstorms at night, heavy rainfall in the day, gusts of wind (City in the Sky-esque), and maybe even some snowfall (probably stretching a little too far with that one.
On other additions, well I don't really want them to change the core game too much as all I really want to play is a more visually appealing version of one of my favorite games. Though I think there are a few additions that couldn't hurt. For one, I'd love a hero mode because let's face it the game isn't exactly difficult (like the majority of Zelda games). So a new mode that adds a bit of difficulty would be welcomed. Also I'd really like an idea that I've been toying with in my head and that's online play. Calm down, not multiplayer, but basically online features. Have a dungeon rush mode to see who can get the best time on a specific dungeon
(have global leaderboards) and maybe a mode to see who can make it through each dungeon consecutively with limited lives. Would really add a lot after completion.
Also for a special edition, please give me the original soundtrack on disc.