I thought I would turn around Jason's thread to ask the same question another way.....
For its time, what was most Original or Radical GCA Idea of All Time? Reading Cornish and Graves, I recall that doglegs, separate tees, courses away from the seaside, etc. were all radical departures from what went before.
As far as individual holes or features, the first things that come to mind are:
MacKenzie's Sitwell Park Super Contoured Green and 16th at Cypress Point
CB MacDonald's Lido Hole (with Cape Hole not far behind)
Alison's Double Green system in Japan.
Pine Valley's Double Green
Whoever used two separate tees, widely spaced for one hole to change its playing characteristics
C and C's huge, blind, par 3 green at Friar's Head.
First large scale use of lakes, such as in Florida
First Desert CourseDesmond Muirhead's Symbolism, although I hate to focus this thread on anything that is gimmicky.
What have I missed and what do you think were original for its time?