From Merriam-Webster dictionary:
Gimmick (n)
a. an important feature that is not immediately apparent
b. an ingenious and usually new scheme or angle
c. a trick or device used to attract business or attention
Most are thinking in terms of definition C, but for Nintendo-originated gimmicks, it usually turns out to be A and B. See: steering-wheel-style-grip controllers, D-pad, analog stick, rumble, wireless.
Sky Render - Sanity is for the weak.