This is a discussion of the style behind my 'Worlds in Collision' campaign. I would like to avoid using any sort of jargon, but instead talk in plain English about my thought processes, intentions, and reactions as GM. The campaign was run in 1989, during my sophmore year in college at U of Chicago.
My idea for the campaign started with a "what if", which was in the back of my mind in high school and gelled during college. I had been running and playing Champions games for some time in high school and in my first year of college), but I was not a superhero comic fan at all. So I started with the concept: how could such superpowers realistically exist? Labelling it as "genetics" or "psionics" is an insufficient answer since that doesn't answer how such powers would operate. I started to consider some possibilities. Beyond the nature of the powers, I put some qualifiers -- I wanted the individuals who wielded those powers to be powerful in a larger sense (i.e. not normal schmucks with powers).
My early notes resembled a comic book to some extent -- especially having holdovers of characters I liked from earlier Champions games. I originally had the idea of a crystalline key which was the source of all powers. However, in college I purged all such influence from my notes and started a new binder. Later, this binder was referred to by my players as the "Big Book of Paranormals".
I came up with a coherent concept for what actually caused the powers. There was a parallel dimension with an altered time rate, so it was essentially an alternate Earth many centuries in the future. Their technology of "virtual machines" would seem entirely like magic to us. As to how to make those into superpowers, that is a long story: essentially a disaster in that world leaves the "virtual machine" under limited control. You can read my explanation.
The important point for style was that everything had to work from this central idea. Superpowers were limited or twisted forms of what were useful functions in a post-technological-transcendence world. For example, any physical attacks had to be originally meant for something else, since physical warfare was long since obselete. From the basis of this backstory, I carefully worked on what paranormals appeared, their history, and what the world's reaction to them was.
Quite frankly, I spent far more time developing the complete history of the world than on anything which my players did. Heck, I spent time working out the lives of paranormals who had died before the game began. There were less than 200 paranormals in history, and I was determined to have an outline on every one of them. In fact, some of them just had a name a blank section in the notebook -- but I'd say at least 75% had something significant.
My overall view of the game was to design a world which had enough stuff going on that it would "run itself". Rather than coming up with adventures for the players, I would simply drop them in and say "do whatever you want". Because of the depth of creation, whatever they did would presumably lead to results which were interesting to play out.
When the campaign rolled around, I decided to choose a premise to push the PC's together and get them introduced. This was certainly a dramatic nod -- the campaign was before I had a good concept of party planning, otherwise I might have let the players determine for themselves what held them together and how they started off.
My premise for the campaign was that the PC's were a group of paranormals who were contacted by a man who had escaped from a powerful secret society -- who wanted their help in finding out what it was up to. Now, as it turned out, they ignored that premise -- the shared knowledge was enough to pull them together, but they never did investigate the Society. Instead, they took off in a completely different direction.
Frankly, I had no idea what interested them -- I had been designing this stuff not as plot hooks per se, but rather as ongoing action and conflict between the NPC's. My premise was such that there was lots of interesting stuff going on, primarily because there were 70+ NPC's with similar powers as the PC's who were also poking about, with their own projects, goals, etc.
Thus, when the PC's decided to go talk to with some Washington-funded paranormals, I knew who they were and had some idea what they were up to -- and with some time to prepare, I filled in the details.
It was not a perfectly realistic campaign. There was a bunch of hand-waving explanation of how superpowers worked (a bit like FTL in a sci-fi game). Aside from the powers and the whole backstory to them, I had two main differences from the real world:
My basic assumption was that most, if not all, of the characters are going to be paranormal. This is immediately a restriction on character generation: all the paranormals have certain personality traits in common: they are highly intelligent, competant, and self-willed. They are generally curious by nature - poking into any sort of secrets and activities they can find. In addition, the PC's needed to be the sort of individuals who would stick together (for practical reasons).
The intent was for a fairly pro-active sort of campaign. I had set things up such that paranormals would by their nature get themselves involved in interesting activities, but what they actually do is more up to them. I can give anecdotes, like: