It'd be hard to sum up the criteria without reprinting most of the article. Basically, it's rated G, PG, PG-13 or R, to use the MPAA guides. Although it's not very clear-cut from his examples, as in theory the mature game is R, but most of his examples are PG-13. In theory the vile game is almost NC-17, but his examples range from PG-13 to actually NC-17.
But I'd say you can equate his ratings fairly well in spirit to the common MPAA ratings, even if his examples don't work very well. That is, light-hearted is pretty much G, standard is probably PG, perhaps leaning towards PG-13, mature is somewhere between PG-13 and R and vile is R with perhaps dips into NC-17.