I'm reasonably sure that the vast majority of people reading this will know what traditional tabletop roleplaying games are like, but since Fiasco is less well known. You can watch Wil Wheaton and others playing a game of it to get a better idea, but for anyone who's wants a primer but doesn't want to watch a long video…
To describe it briefly, you start by rolling a load of dice, and picking from the dice to work out relationships between characters, and important objects, locations and needs, then you start playing scenes between two or more characters as their plans build up, and then explode in their faces. The dice limit (though don't utterly dictate) the setup, then are used during the game to mark whether scenes have gone well or badly for you, and they're rolled at the end to determine how good or bad your eventual fate is, but the individual scenes are purely descriptive, there's no mechanics for working out if you succeed in an individual action, you just describe it individually or collectively.
Having played Fiasco several times, and comparing it to a few sessions of the Slaine D20 RPG, her response was:
first impressions of role play games was that they requires hours of commitment, character development where learning how to fight required homework. Intrigued by the comics and the basic backstory I was interested wanting to see how my character could develop but put off the complexity. More so the commitment needed to see those games through.
Taking out the gamemasters and limiting the number of scenes is a real advantage.
I found [Fiasco] a real gateway into a world of gaming.that would otherwise find too intimidating and closed off.
Whereas my perspective is that I enjoy an occasional game of Fiasco, but it couldn't replace my weekly Exalted or Pathfinder games, as I just don't find enough depth in it to hold my attention in a more regular slot, and a lot of that depends upon those rules, and the gamesmaster behind them
A lot of this does come down to the gamist/narativist/simulationist divide of roleplaying — are you after challenge and achievement, telling an awesome story, or building a world that feels real?
Obviously everyone falls somewhere in the middle, but it was the (reasonably strong) gamist part of me that found it somewhat empty when my Fiasco character Maxwell Billingham-Smith (late of the Shadow Cabinet, now a zombie hunter) was chopping down zombies left and right whilst being interviewed on the nightly news, or when he crept out of the zombie infested Tower of London — both were situations of risk to the character, but the descriptive nature of the game meant I was in control of whether anything bad happened to me.
At their best, roleplaying games can combine the sense of victory and achievement you find in a tough computer game, with stories that rival great films and books, and with the opportunity to put yourself in someone elses shoes, someone who might have a personality completely different to yours, or might be yourself with certain aspects exaggerated, adjusted, or allowed to run free.
In a Pathfinder game I play on Mondays with a few friends, we were recently trying to free a city from the people who'd taken it over, and were squeezing it for all it was worth. Because of the power that the D20 system gives to high level characters, combined with a lot of careful planning, we were able to retake the city within three days — decapitating giants on the first night, gassing guards on the second, finally on the third day rescuing the rightful ruler and variously killing, chasing down, and offering a job to the people involved in the usurpation.
This took us a couple of gaming sessions, and I'd say we spent as much time planning what we were going to do as we did in the actual encounters themselves; it was all about using all our various capabilities, predicting our opponents, and playing the odds. There were many moments where it could've gone very badly for us, and several moments when it nearly did, and it's because of those moments that our eventual victory felt awesome.
And to bring this back to the posts title, the gamesmaster is critical for that sense of victory. Yes, a chunk of it comes from the rules, from the base potential for failure inherent in 'Roll to hit'. But a lot of it comes from the man behind the curtain, from the person who knows what our enemies were doing whilst we were planning, who presented us with the situations and workout out the fallout from our successes, and who ignored what the preprinted adventure said, instead deciding that the bad guys (having lost most of their fighting forces in two nights with no visible source) would try and execute their hostage, forcing us to try and rescue him, despite having spent most of our resources on dealing with the aforementioned forces.
Roleplaying games, whether GM'd or not, allow you the opportunity to try and do anything you can imagine. But it's the gamesmaster/storyteller who brings the real surprises, the twist that has been been quietly signalled ahead of time, and who can judge your strengths and throw just the right level of challenge against you.