Flexibility
Expounding on the previous point further, the clear goals and expectations of the base Pac-Man formula make it an attractive game for all skill levels. But beyond this, its simplicity also allows for an element of flexibility and adjustment to be made, in order to entice repeat purchases time and time again.
Looking at the aforementioned iOS app, it features a selection of new maps to freshen things up. This doesn’t compromise the simplicity, but builds on it in a way that feels natural and reasonable. Sometimes, more bold design choices are made, to mixed results. In Ms. Pac-Man, the behavioural patterns of the ghosts was adjusted to include moments of chaotic randomness, thus preventing a knowledge of their movements as a predictive path to success. There were also other minor aesthetic improvements made, in addition. Once again, nothing that broke the mold, but enough to enhance the experience as a whole. Pac-Man Jr. expanded the maps so widely, it required a moving camera to track the player. Not quite as user-friendly, but again, not overly obstructive.
Another thing worth considering is that the listed examples weren’t even officially licensed Namco games. The Pac-Man formula is pliable and enviable, to the point where other developers looked to ride the wave of success. One can only imagine how many Pac-Man clones exist out there, each with their own quirks to differentiate themselves.