It's a Fantastic game. I just beat it, actually. And I did absolutely 100% everything that there is to do in the game. Great game. I wrote a quick review on it here..
What Wii U games have you beaten?
I plan on writing out more reviews for all of the games that I have beaten. But, bear with me, as I need time to actually write them out. But I plan on giving my honest opinions each of them. Some are better than others, and I'll go into depth on all of them.
Feel free to go there for the review. However, to give a quick answer for you... The sailing is faster. Some treasures and prizes have been moved around. The Tingle Tuner was replaced with the Tingle Bottle, for a more Miiverse active game. It looks fantastic. Tho, there aren't any new items, dungeons, or characters. In fact, the dungeons that were cut from the original game were actually used in later games. So they couldn't be used for this game, as they would be the exact same levels as later Zelda games. Also, they added Gyroscopic motions, for more Wii like aiming, for accuracy. Works great. There's a new Hard Mode, where there are no health hearts. Only potions, fairies, and your grandmothers soup, can heal you. Also, enemies deal twice as much damage per hit. So, you have to be extra careful in that mode.
In the end, it's a great game. It looks great. It controls great. And it's as fun as ever. I do recommend it. I have both, the original Gamecube, and this new Wii U HD version. And I have now 100% completed both entirely. The Gamecube version is great, but the Wii U version I would say is better. The visuals are better, the sailing is faster, gyroscopic movements are a great addition, the Miiverse interactions are fun, and make the figurines easier to get, and the hard mode adds a nice challenge to the game as well. So, yeah, I'd rate the new Wii U HD version as overall better than the original Gamecube version.
Hope that helps. If you need to know more, read that link. Any questions, just ask. I'm always around.