So far, I have three -- Complexity, Potential, and Efficiency. Complexity is partly a count of words in the text, with extra points for complex abilities. Potential measures how many words having to do with direct game mechanics are in the text (and I'm starting to think potential should be measured as a percentage of the full Complexity.) Efficiency is meant to measure how much bang you get for your buck -- which is to say, how much power you get for your mana.
Results with the complexity metric are encouraging so far, but not so much with the potential metric. I'm going to modify it so that Potential is a percentage of Complexity and then move from there. I'll need a new formula to calculate Efficiency, but I needed one anyway.