I joined the RPG world relatively late in the game (and I mean "real" RPGs here I had played Zelda and other games with RPG elements) with Final Fantasy 7 in 1999 or 2000 for the PC.
So, unfortunately I wasn't there for the evolution of the RPG. Since then however I have played tons of them, most have been console RPGs as opposed to PC RPGs.
So what are some revolutionary concepts (or good ideas that never took off) you've seen in RPGs, the games you've seen them in and why you liked them?