Just had a great time with my old rpg group (we havent played together since.. dont know, college ? ). It was good ol´ Shadowrun in the 2050´s, a setting everyone in the group knows as the back of their hands.
So, nowadays I dont have much time to prep adventures and the like, and coincidently I just finished reading this "Apocalypse World", a game that advocates a more or less sandboxy style of gaming and even gives techniques for implementing it. So I tohught: why not try it? Well, I did - the night before I spent 10 min taking some notes and memorizing some tips from that book (including the one that says "Do NOT make/plan any adventure!").
So there I went..
And shit, it was awesome. The situations arose from the players own agendas and interactions with the setting, and I as a GM just reacted, adapted and improvised. In the end, we had a great web of plots and hooks and even a big adventure in place, and I never created/planned anything beforehand. You guys should have seen the smile on my face. ;)