I have this project for a computer "role playing experience" (rather than "role playing game"), and I'm not sure how to approach it. Key elements are:
* unsettling horror thematic;
* hallucinations play a major role; players shouldn't be sure of what is "real" and what is not;
* focused in plot advancement and not on character advancement (hence, "role playing experience");
* puzzles and decision-making make most of the gameplay, and combat should be avoided if possible (usually lethal?);
Thing is, what kind of game should this be? I want it to be browser-based. The reasons for that are that browser games are easily accessible by anyone with internet, no dowload is required, and it's easier to promote. It does mean, then, that it won't be real time, but turn based. This brings in a challenge: I don't want players to log in and find someone killed them while they were out, or even between page refreshes for that matter.
One approach is similar to the Polaris RPG "diplomatic" resolution system: You somehow have to "accept" the incoming attack, or it won't happen. But then, life's just too easy.
Another challenge I face are the hallucinations. Not mechanic-wise, but design-wise. If every player is hallucinating, then the hallucinations are normal and could be considered somewhat "real". So, for players to feel like they're insane, there must be (mostly) sane people around, right?
Sometimes I think this concept is better for single-player (as in Silent Hill), but the idea of two human characters seeing each other as monsters appeals a LOT to me.
Forgot an important detail, the "lone multiplayer" deal; the thing is, the game should feature and endgame, which is personal to each character. The point of the game is to escape from the hallucination world, but first characters must understand why they're there. And each character has a different reason, which is determined by random (and secret) stats generated on character creation.
So, although all characters are generally pursuing the same goal, each is on his own, for his specific goal is different from all others.