Earlier quoted context omitted.
> They're a great demonstration of how the illusion of progressing at something is all you need to keep people interested, even when the only thing they're progressing towards is... the opportunity for more progression. If anyone wants to try this type of "game" give cookie clicker a try.
One more with the niche of this forum, and one that doesn't take that much time (depending on your take on the task), is Paperclips http://www.decisionproblem.com/paperclips/
This game works so well (within its scope) because of its ability to surprise you with the crazy narrative and convoluted mechanisms it brings in as you progress.