One of the most successful videogame formats of all time is the computer role-playing game (cRPG). The basis of all such games is a progression structure which functions as a reward schedule (providing a steady supply of the "reward protein" dopamine, and the promise of future reward), which is one of the key reasons why people play videogames.

This list is from an original post on International Hobo's site. For more information about this list and to comment on it please see the source post (linked below).