If this game has an actual gimmick to it this time, i'd guess it hasn't been shown yet, and probably won't be until the next trailer. Every Major Zelda game has 2 tiers of trailers that each show us different things. Phase 1 shows us overall, general mechanics, visual style, etc. In this case, the open world, the emphasis on explorarion, and arrow focus. Phase 2 shows the game mechanic that is tied to the story, which we haven't seen yet.
Ocarina of Time:
Phase 1: Jump to 3D, 3D environments, aiming bow/arrow vertically also, instead of horizontally.
Phase 2: Child/Adult link, time travel, Ocarina songs, Epona.
Wind Waker:
Phase 1: Cel shaded graphics, dodge/counter mechanic
Phase 2: Sailing the ocean, using other weapons, etc.
Twilight Princess:
Phase 1: Big hyrule field, horse combat, dark theme with realistic (non-cel shaded) textures.
Phase 2: Wolf Link, Twilight enemies, etc.
Skyward Sword:
Phase 1: Motion control sword (sword combat focus), bow, Running mechanic. Bomb bowling, beetle item.
Phase 2: Loftwings, Timeshift stones
A Link Between Worlds:
Phase 1: 3D with vertical dungeons, ALttp overworld/combat.
Phase 2: Wall merge mechanic
Zelda Wii U:
Phase 1: Open world, multiple arrows, time-slow mechanic
Phase 2: ???
Skyward sword is a bit of an exception, but its intro trailer showed more than most zelda trailers do when they're first revealed. I mean, it showed like 5 items and how they work with motion control. Generally speaking, I don't think we've seen the 'REAL' twist/mechanic this game, and we probably won't until E3 this year.