Edge of the Empire is my favorite roleplaying system by far. The dice are so intuitively helpful in creating a story with your players that I rarely need any prep work at all. I completely ad libbed a heist with three players, and it worked out wonderfully. The girl who only cares about combat got a shootout and a car chase, and the two guys who are really into carefully executed plans and RP managed to break into a high security office building owned by a crime syndicate and run off with tons of info after fattening up their bank accounts. It was a perfect, collaborative gaming experience that was facilitated by the dice system.

And it was so much freaking fun!