A Game for GMs?

Yesterday I tried a new thing. Once in a while, my players ask me to improvise a game. They give me some elements (usually genre and tone), and I run a game around based on them. Yesterday, it was a post-apocalyptic high fantasy comedy game.

The game itself wasn't all that interesting, at least not to write about it anyway (although it did include an electrical tiger blowing up a 40 meter long dragon), but I tried a new mechanical trick. It was very simple: During character creation (which was done collaboratively by all players) each player chose 2 events that changed the life of the character.

Then, at certain points in the game, there was a role switch: The character had a kind of a flashback to the event; one of the other players (or me in one incident) played that character (in that event), without knowing how it is supposed to end; the original player GMing the flashback scene, with the goal of making it come close to what he originally envisioned, without railroading.

I think it went really nice, and added a lot of tone and comedy to the game, but as with any experiment there were a few things that weren't done well. The most important one was that the other players railroaded too much. The second thing was that the players didn't know when to end it, and sometimes it felt too long. Luckily I was there to stop it when I felt it was enough, but it felt like a forced conclusion.

I don't know yet if I'll ever do that again, but I'll make sure that I have fellow GMs as the other players. I think that their understanding will surely help to reach a fuller potential of this technique.

Has someone tried something similar to this? How did it go? Any tips will be welcome.