CrimsonCavalier
Fuzzy Pickles
My list of gimmics for each Zelda game would be as follows
Zelda 1 - Overworld/Underworld, 1st/2nd Quest
Zelda 2 - Spells, XP, the most open overworld of any Zelda game to date (in my opinion). Can't really say 2D platforming as that was a directional change for the series that in the long term failed hence Zelda 3 went back to top down.
Zelda ALTTP - Light/Dark World
LA - Jumping with Roc's feather, 2D platforming sequences (was a gimmic here)
MC - Kinstone fusions, the figurne lottery, big and little Link and the 4 Links
OOT - Two Time zones, fishing and the overuse of the ocarina
MM - 3 day cycle and the masks
OOS - Seasons
OOA - More time travel
WW - Sailing, all that damn fishing up junk while on the boat and the Nintendo Gallery
FSA - the 4 Links
TP - The wolf, the normal/twilight areas and those fancy secret sword moves you learnt (and motion controls in the Wii version)
PH - More sailing.
ST - The train.
SS - Grinding/farming all those materials, Above and below the clouds - the two different areas.
ALBW - Two worlds and the merging with walls mechanic
The gimmics just make doing the same core thing over and over in every LoZ game interesting. Most Loz games are completing dungeons/palaces/temples, getting tons of loot to do so, and finally beating an end boss to save someone or something.
Would you consider those gimmicks or gameplay mechanics? I don't think the two words are synonymous.