Minecraft : One of most successful games ever made

Minecraft has an art style that lots of people find pretty rough. It is very light in gameplay, focusing more on creative aspects. It isn't on Steam. It doesn't do discounts, and actually gradually raised its price. 

It is written in Java with all the baggage that goes along with it. Notch took quite a lot of time off during development.

If any other game developer were to emulate Minecraft, they'd fail badly. And yet, Minecraft is among the most successful games ever made.