How did you go about designing the Heroes Against Darkness solo adventure? Did you start with a list of rules you wanted to teach or did you begin with story?
The mechanics and the story for the solo adventure developed kind of organically, as it turns out.
The rules were already in place, and I had seen the solo adventures from the Pathfinder and D&D Red Box solo adventures, so I wanted to do something along those lines for Heroes Against Darkness.
I'd been a fan of the Fabled Lands solo gamebooks for a while, and realized that I could use the mechanics from that series of books to make a truly non-linear adventure, which none of the other games had really managed.
There are only three main mechanics in the game, Ability Tests and Combat/Magic (and healing too), so covering those was pretty much a no-brainer.
Ability tests are straight-forward enough, with players just rolling their character's ability modifier against a difficulty number. But combat is more extensive, with magic and physical attacks needing to be covered, as well as magical healing for the hospiters.
I'd already used the location of the adventure in the ongoing monday-night campaign game I'm GMing at the moment. So I figured I'd reuse my maps from that adventure for this solo adventure.
Re-using the maps turned out to be tricky, because all of the maps for party play are the wrong size for a solo character to run through, and I wanted to make sure that each of the maps for the solo adventure could be printed out on a single A4 or Letter sized sheet.
The other challenge was to balance one Level 1 player character against two or three enemies in each encounter. When player characters only have 18-20 Health Points, they can get killed pretty quickly. I eventually managed to balance the game by reducing the stats of the monsters and making most of them minions, who have minimal Health Points. The other way I balanced the adventure was by including healing potions through tower, just to give players some help as they progress.
Come try Heroes Against Darkness, the free, fast and flexible modern d20 RPG:
I think the best way to teach a ruleset is in small, manageable chunks with good examples. If the ruleset can be partitioned (such as vehicle combat or hacking) then those sections should be distinctly explained with examples of different facets in action. It is important to note that roleplaying games are used as a book to be read but also (more often) as a reference. Each example should be neatly self-contained so that it can be used around the table when a ruling clarification is required.
Although enjoyable, I think a solo adventure should act as a fun aid to learning a system, rather than being the core method of doing so. Experienced GMs (which make the majority of those downloading a free RPG) will not be able to skim read the solo adventure to get a sense of the rules like they would a rulebook. As much I am against the organisation of most RPGs (especially including fat lists of things in amongst the text), I do think that the old fashioned manner of explaining a rule and then providing a short example of its use is important.
@CptPhoenix, wehen Cyberstalking, you're not supposed to let your quarry know you're doing it.