Well, if this game is truly as "open world" as Aonuma is hyping it, I really hope they not only pull it off with style, but pull it off with the typical Nintendo standard of game-breaking bugs kept to a minimum. With the increase in scope and environment, that's really my biggest concern right now, considering this is looking to be on the scale of Skyrim. We all know how well Bethesda bug-tested that game, so I hope Nintendo can put them in their place with a relatively bug-free release.
From a design standpoint, I'm not fond of Open Worlds of late due to several other games I've played recently (Skyrim, Infamous SS, Saints Row 4, Assassin's Creed 4, Watch Dogs, etc.). Traditionally, they tend to be vast wastelands of nothing dotted with quest markers and collectables. I get hooked for a few hours, and then burn out hard by the end. I'm very wary of this change, but it is a change the Zelda franchise needed to keep evolving. I just hope that Aonuma and his crew are working on avoiding the usual Open World pitfalls of boredom and copy & paste design. I also hope they don't fall into the trap A Link Between Worlds did, where being able to go anywhere after a certain point meant that the dungeons all had to be designed to be completable with the least experience and skill possible. It resulted in particularly bland dungeons and lame bosses, so I hope the experience taught Aonuma to find a middle ground with the Wii U Zelda.
Overall, I'm cautiously optimistic. They seem to have the right idea. I just hope they can nail the execution.