Take everything that's great about open world games, then add Zelda, you know, one of the greatest game series out there. That's a fairly exciting mix. It's not "just another open world game". If the trailer is all you've seen then you're in for a serious treat, the actual gameplay is far more impressive.
Absolutely. Game of E3 by miles.
Compare it to Horizon, probably it's closest contender for the title, I know which world I'm most excited to explore, and it isn't the one with robot dinosaurs.