System
Notes:
The simplest system ever: Characters have skills/stats. Difficulties are set by GM according to a standard range. If the character has a high enough skill, they succeed. If their skill is too low, they fail. Amber works this way. No Dice. No random chance. Becomes storytelling rather than gaming. This can be fun, but it's not what I'm looking for.
The worst: Roll percentile (or other large flat range such as d20) to determine success or failure. Character skills/stats have negligible effect on the outcome. Virtually pure chance. Range simply shifts up as character gains ability. D&D works this way at low levels. At high levels, most static difficulties can almost be ignored.
Most system fall somewhere in the middle. GURPS has a nice bell curve. Success based, difficulty based, etc.
Idea:
Start with the simplest system ever and add a Player Determined Risk Factor.
Skills range 1-10 1-20.
Static difficulties in standard range, up to 40 for supernatural/superhuman.
Risk Factor: The player rolls 2 dice of the same type. One is designated positive, one is designated negative. Range = -(dX-1) to +d(X-1). Add this Risk Factor to Skill to determine total.
Allow Players to determine risk factor within range, GM can set minimum risk factors.
Risk Die can not be greater than base Skill.
Example: I have a skill of 5, I can take a Risk Factor of ZERO and my final result is 5. I can take a d4 + d4 for a total range of 2-8. If the task is sufficiently risky, the GM may set a minimum risk factor of d4, requiring a roll.
I have a skill of 20. I can take a Risk Factor of ZERO, d4, d6, d8, d10, d12, or d20. YOU DECIDE HOW RISKY YOU WANT TO BE. Taking a chance can screw you over, or save you. The maximum range is always 1 to (2*Skill)-1
Another example: Your skill is 8, you choose to take a risk factor of 4, your mimimum roll is 5. Your maximum roll is 11.
The curve is triangular, but the average result is ALWAYS your base skill, and the range is set by you. Weird.
Consider open ended dice under certain circumstances? Allows for BOTCH and CRITICAL.