I am not an early buyer.
I usually wait for reviews to get at least a general idea of the games quality.
There are so many good games, that I do not want to waste my time and money on a bad one.

As for the next Zelda:
So far my only concern is the "open world"-like concept.
In the demo-gameplay footage the world seemed too big and too empty. There were a few individual places of interest (like a lone building or a camp), but with a lot of empty fields, forests or rubble in between.
There were no hordes of enemys like in WOW to fill the massive places.
There were no killer graphics like in Firewatch, where you can just walk around and marble at the environment / atmosphere. (Although the graphics are OK and fitting for a Zelda game.)
I don't see how Zelda is going to fill this huge world.
It might get annoying very fast, when you constantly have to rush through boring nothingness to get to the next interesting spot.