Erez is right about what a learning curve is, and Roberto is right that it is not uniform for all people. But I hesitate to call it a subjective measure, because it is dependent on external, measurable facts about a game, not just on a person's subjective experience of a game. These facts include similarities to and differences from known games, overall simplicity or complexity, and volume of details to remember. The qualities that contribute to a low learning curve are similarity to known games, simplicity, and few details to remember. The opposite qualities contribute to a high learning curve. Of these qualities, only similarity to and difference from known games will differ from person to person. When a new game is similar enough to other games, this can make a significant difference in the learning curve for that game from one person to the next. For example, Roberto would have an easier time learning an Ultima-style game than I would. But when a new game isn't similar enough to any previous games, everyone is more or less on an equal footing with respect to learning that game. Regarding Attendence Chess, its pieces are mostly different from the pieces I know of from Chess or any other variant. The high learning curve comes from having to memorize the powers of movement of several new pieces, and I expect this will be true for nearly everyone, since, as far as I can tell, most of the pieces are completely new.