The randomness in RPGs (dice rolls etc) I think really provide something that's not provided in other entertainment media, which is that no one necessarily knows how the story is going to turn out before it's over. In an old game of Warhammer Fantasy, an NPC critically failed a stealth roll and it completely changed the rest of the plot because the PCs captured and interrogated him and thus learned way more about what was going on then they otherwise would have at that point. I definitely did not plan for that to happen and it made for a much different story, but just as interesting, story as I had originally intended.