Well, things normal zelda games don't/didn't have, like zelda II, the only real sidescrolling zelda. Or if it implements something new, like Magic spells, or extreme puzzles, or a non-triforce related story.
though, it doesn't have to be revolutionary to be great. It could be just like the other zelda's too; which proved to be a winning formula. I think the lowest rated zelda game ever was 8/10 which was that crappy spirit tracks one, which proves the classic style can work well