The tech demo was easy to make because they simply adapted the Twilight Princess style to HD. As Aonuma confirmed when Wind Waker HD was announced, they were also experimenting with various art styles while in the process of designing a brand new art style for the new Zelda game. They were very upfront about this from the outset, never ever suggesting that the game would resemble the tech demo. The new art style has much more effort put into it than the tech demo, and it shows, as the new style is significantly more visually appealing.
I wish everyone would simply accept a much better-looking game than the one they think they were promised.








