Rate of Character Advancement = 1 / Character Capability
Something like this was an assumption of early D&D, but it has been lost. In today’s D&D, as it is meant to be played, you advance a level every 11 balanced encounters or so, and each level is roughly balanced with every other.
Who knows what tomorrow’s D&D will bring? Well… we might have some ideas. They’ve suggested that the level advancement rate is still constant, but that the “sweet spot” has been extended. To me, this (along with hints that multiclassing is a wholly different thing than it once was) suggests that they may have abandoned the idea of keeping the difference between different levels constant. This isn’t a post about 4e, though. This is a post about the Experience Equation – and why something like it is a good thing.
The basic idea: With the Experience Equation, you can give someone the choice of playing a novice or a veteran. The veteran is more capable, but less flexible in development – he’s going to advance very slowly. The novice is rewarded for being less capable at the beginning by advancing more rapidly. D&D recognizes this even in its current incarnation, though there it is instituted through the Challenge Rating system, which has always felt a bit clunky to me.
The advanced idea: Character Capability is not necessarily the same thing as Experience Level (or its equivalent in other games). I’ve been thinking a bit about that one-on-one gaming thing. Combat in a one-on-one game can be pretty deadly – particularly because the game wasn’t really designed to support it. Why not give your player a bit more meta-control? Give your player an unlimited number of Action Points. Allow them to be spent for something like Second Wind in the Star Wars Saga Edition (an instantaneous healing thing). The catch? Every time you spend an Action Point, your experience for that encounter is divided in half.
Other applications? I’m sure there are a ton.