The Legend of Zelda: The Wind Waker HD amazed me from start to finish. The first thing that impressed me was the graphics: I have played the GC version a bit before, and my view is this: the GC version had a great idea with the cel-shaded graphics, but didn't have the hardware to make it truly beautiful. The Wii U version keeps the cel-shaded idea but now it looks the way it was meant to from the start: incredible. You will definitely be impressed by the beauty of the game, even if it is a little more "kiddie" than Ocarina of Time or Twilight Princess.
The story was the second thing that amazed me. While the story may seem pretty simple at the start (rescue your sister from a giant bird), by the end it will be so complex and deep that you can't help but feel a duty to make sure things end the right way. There are twists and turns until the very end.
The combat is good also. The Z-targeting system makes combat easy to follow, and you really feel engaged with your enemy, not like you're slashing your sword randomly.
Also, while the Wii U GamePad gets a lot of hate, it enhances this game in a big way. In the GameCube version, you had to pause the game to check your map (which you will do a lot) and change items (which you will do even more). In the Wii U version, however, you can do these things on the GamePad in seconds, no pause required. This makes the game flow much more smoothly.
The dungeons are also very impressive, with clever puzzles and boss battles that will challenge you. There is also an added twist in some dungeons of teaming up with other characters in the game and using their abilities to help yo complete the dungeon.
The sailing is truly a unique way to explore a Zelda game, and I enjoyed it a lot. While it may have been tedious on the GameCube, the Swift Sail makes it much easier and quicker to travel to different islands in the Great Sea. Also, the music while you're sailing makes you feel heroic and courageous, not bored.
The only flaw I can think of for this game is part of the main quest, near the end, in the Triforce quest. I had to use walkthroughs and hints for a lot of this quest, and it takes a lot of time and effort, even though it was shortened from the GameCube version. I didn't like it because it feels like you are so close to the end and that you've already worked so hard, but then the game forces you to sail around the world for hours. To me, it feels as though Nintendo needed more hours to add on to the game, and rather than add a few dungeons, they added the Triforce quest. This is the one part of the game that feels like Nintendo has been lazy.
However, I would say that it is worth it. I am glad that I hung on and finished the Triforce quest, because I loved the ending and it concluded the story very well. While you may have to put in some ard hours for the Triforce quest, the good overwhelmingly outweighs the bad.
To someone who has already played the GameCube version, I think playing it over again on the Wii U with immaculate visuals and the advantaged provided by the GamePad would be totally worth it, even though it is really the same game. To anyone who has never played the Wind Waker, I would advise you to play this version: It is a nearly-perfected version of a game that was already incredible. It is truly a Zelda experience unlike any other.