Last night I was going through a binder with my WEG Star Wars materials in it. This was the last game I played with my group before we all began adventuring in our often exciting adult lives. That would have been 1991 the year I began my university fine art education.
What I noticed was that I had paper clipped together a number of loose leaf sheets that contained a mash up of a title, simple maps, NPC drawings, sparse notes on encounters and even scrawl made during combat resolution. Looking at these I was reminded that these single page notes had been the fountainhead of the best sessions we ever played in that game. A cover sheet for these pages reads "M.U.A.Y.G.A." Make Up As You Go Along.
Recently I've been putting together a collection of notes about my original D&D campaign, the hope being to recreate some of the best adventures I ever ran for my group back in 1982-83. Those adventures also had a made up on the fly element to them, the original maps had notes written right on them and most encounter details were written in the rooms themselves.
Why were these adventures so popular with my players? Partly I think it was because they were tailor made for the characters in the moment. If the players looked bored it was time to imagine something really exciting, and that related directly to their character. This was especially true in the Star Wars games. But what I really think they liked was the fast pace and not knowing what to expect. Anything could happen and because it was a stream of consciousness thing happening on my part the most absurd things did. In D&D (1983) I remember them really liking being chased around dungeon corridors by a steel wall with spikes trap. It would pop up randomly and characters would have to save vs. death. In Star Wars (1990) the characters were pursuing an NPC over a series of heavily grassed asteroids with an atmosphere, jumping from one to another (kind of sounds like Super Mario Galaxy).
What made it fun for them was the fast paced fear. Not horror. That's something different. What my players liked was Dungeon Panic.