With that in mind, when I talk about adventure structure, I'm talking with the standalone episodes in mind. This is not because they're the better ones (in fact, they usually aren't - Supernatural's arcs are what make the show for me) but because they make a solid foundation to build on. Once you can do a solid monster-of-the-week game, you can build from there to other ends.
The thing to consider when talking about the structure of games is that, like Leverage, the most important element is information management, but unlike Leverage, Hunters start out much more in the dark about what's going on. At the outset of the game, they discover something bad is happening somewhere and go to investigate.
HOW DO THEY FIND OUT
1. News Report of Strange Event
2. Many news reports of seemingly unrelated events
3. Rumor among truckers and travelers
4. Mystically Portentious Sign
5. Contacted by friendly Hunter
6. Contacted by another Hunter
7. Contacted by former hunter
8. Stumble across it
9. Become Victims
10. Contacted by mysterious forces
WHAT SORT OF BAD THINGS
1. Local disappearances
2. Traveller disappearances
3. Pattern of Deaths
4. Exotic Deaths
5. People seeing strange things
6. Odd Behavior
(This could probably get fleshed out to 10, but I'm not sure how many ways I can restate "Weird deaths or disappearances")
Once they find the problem, there is usually a period of time spent looking at what has happened and trying to figure out what could have caused it. This period might be very short or very long, and it will shape the episode. Basically, the "hard" part of the episode is going to be one of the following:
- Finding out what the creature is (and by extension, its weakness)
- Get their hands on whatever they need to exploit the weakness (get the arcane widget, find the body, find the lair)
- Applying the fix (Actually shooting/burning/stabbing/whatevering the thing, performing the ritual or the like).
In RPGs, there's often a temptation to make all three of these the hard part, and the result is adventures that turn into long slogs. By making only one of them the real problem, pacing stays pretty sharp, and the formula becomes MUCH more usable. If the problem was ALWAYS that the monster was unknown then every show/game would be about research, which would get dull fast. Ditto the other hard points. Shifting emphasis between these three consistent points (Research, Investigate, Apply) gives you the benefits of consistency while still providing versatility.
So that gives us a basic frame. Next thing we need to do is plug in some monsters.