Today Patrick and Nate and I got together for a game of Risus. Each of us are regular DMs, and none of the three of us could be bothered prepping for a game, so we decided on an ad hoc basis to do a GMless game of Risus. Patrick has a rubber dinosaur that he uses as an eraser; we decided that whoever wanted to grab the dinosaur could be the GM at any given moment, and that anybody could pass the dinosaur to somebody else to foist GM-hood on him. (Actually I think I'm the only one who started doing that.) We decided to play a Star Trek game - the basic idea was that we were a threesome of crew members of the Enterprise charged with finding dilitheum crystals on a volcanic planet: this almost entirely stemmed from the fact that I had an idea to create a character who was a vulcanologist who spent his entire life getting pissed off that people assumed he was an expert in vulcans when actually he was an expert in volcanos.
We had a good time. There is something about Risus that just works - a magic in simplicity. A lot of the fun of the game, it must be said, came from the idiotic characters we created. Patrick had a humanoid alien who could vomit multi-purpose chemicals but had a "weird life cycle" that meant at any given moment he might morph from a humanoid into a moth, into a caterpillar, or into a "noble insect-headed alien". Nate had an engineer who was an expert in "teching the tech" but who was also True Neutral and thus unable to ever involve himself in anything decisive. I was a three-eyed vulcanologist who knew nothing about vulcans but who was really good at scanning volcanoes and was born on a prison planet. Together we avoided radioactive feldspar and murdered an innocent entity with dilitheum for a heart, while pissing off Lieutenant Worf.
In any event, I think we proved decisively the adage that system doesn't matter. We had a notional rolling GM and played ridiculously hard-and-fast with Risus's already light rules, but in the end nothing mattered except that we enjoyed creating a stupid story that took the piss out of Star Trek: TNG while simultaneously paying tribute to it. You don't need a good system - you just need people who get along. And a willingness not to give a fuck when things make no sense.