It is an ASCII roguelike game that has a number of different modes. There is an adventurer mode, which is similar to the classic nethack games, but there is also a Dwarf Fortress mode, which allows you to build and design a fortress.
It is like the old dungeon keeper PC game, but with ASCII, and far more detailed (and addictive).
Ok, the graphics are pretty ordinary (it’s ASCII), but if you go to the wiki you will find heaps of information on how to customize your screen with graphics, as well as lots of hints and tips to play.
You start by first creating your own little world, creating mountains, rivers, lakes, forests, and then it populates the game with cities, heros, legends.. 200 years of history.
So far, I’ve lost many a fortress to those pesky goblins, but I’ll build up one to the likes of Moria without getting too deep for the lucrative adamantine.
Each time you lose a fortress, it saves the world state, so you can always go back to your existing fortresses as an adventurer and recover all your stuff.
It just proves that you don’t need fancy graphics or mass marketing to make an enjoyable game – it is all about the gameplay and replay.