Favourite Revolutionary Game Mechanic
I've never encountered any that felt particularly revolutionary...
Sure I like the dice that come with Fantasy Flight's Star Wars RPGs. They're kinda cool and do add something to the game but are they revolutionary? Nope.
Now this might be down to me playing the "wrong games" but I don't thing there are revolutionary game mechanics out there.
Evolutionary maybe, interesting and new quite probably but revolutionary? Nope.
Not even the d20 OGL was revolutionary as a mechanic...
So nope, I don't have one but that's largely down to my not believing there is one... Mind you that probably says as much about the games I like as it does anything else ;-)