Prosperity is a game about growing a city through strategic resource management.
A Text Based City Builder
Most of the time when somebody says City Builder, people think about city planning - where to place buildings, how to get around terrain, etc. Prosperity takes that away and instead provides challenges in thinking about how to balance growth and sustainability. A text based approach reduces complexity in considering how buildings are placed, where people work/live, and what terrain modifications are necessary. All a player needs to know is how much usable land there is remaining, and how to go about getting more land.
Not all city building elements are abstracted however; players must order building construction, and other projects to meet demands placed by people and natural events.
It is a Simulation
One particular philosophy the game tries to stick with is the concept of emergent gameplay through expressing individual systems of interaction rather than directly dictating mechanics. For example, suppose we want a way to model resource growth. A simple method is to have clear numerical values for resource/second based on some combination of factors. Prosperity took a more complex route: resources are created when it is harvested, refined, by some group of workers. Each worker contributes some amount of work, which is derived from some independent variables. A piece of work produces some resource once it is done. This means the mechanism of resource growth and predicting resource growth is itself emergent from more fundamental rules. This piece of logic is complex but it opens up the game to a number of new possibilities - for example having some way to affect production output by making people happier, or considering trade-offs between the happiness of one group of workers with the happiness of another group. We could now model complexity or effort required to do some work based on variables like seasonal changes, migration patterns, maybe even availability of water. When gameplay is emergent from some set of rules that expresses a simulation of a world, the gameplay itself can be wildly different time after time.
It is a Story
Stories drive people to try new things, give hints to explore a mechanic and think deeper about how to use it. Due to the way the system was designed, outcomes can be very different, so while it is a good idea to have some fixed storypoints, the game works better where stories themselves are fluid. Therefore, the game isn't telling the players a story, so much as players are writing their own stories through their choices.