For those of you who don't know, Dwarf Fortress is a fantasy simulation game most similar to dungeon keeper, although not really that much like Dungeon Keeper. The goal is to take seven dwarves out into the wilderness, build a fortress and riches, and defend them from wildlife, thieves, cranky elves, and goblin sieges. The game is made and supported by one person, and is likely the most detailed game you have ever played. Injuries are tracked down to specific organs, fluids spread out to fill the space of their container if possible, and water freezes in the winter. As your fort prospers, migrants come looking to share the wealth, giving you more dwarves to do specialized labor. Eventually tales of your wealth attract thieves, invaders, and kidnappers.
You have a lot of control over your start. You get to pick out which area of the world to start in, from lakeside, to plains, to forests, to glacier. Lack of wood will stop you from being able to craft beds or power your forges. An area with a low water table may prevent you from having access to stone and metal. To compensate for the environment, you are given an amount of points to choose what to set out with. You can bring food, building materials, animals, alcohol, or spend your points to give skills to your settlers.
As the game progress, it gets more complicated. More dwarves will migrate in, eventually putting your outpost on the map. Then noble dwarves will start arriving, and demanding that you build rooms in the fort to meet their royal needs. Dwarves will occasionally try to build an artifact, a once in a life time project demaning that you find them special materials, that will either result in a very valuable object, powerful weapon, or armor, or maybe just a fancy cabinet. If the dwarf cannot find what he's looking for he will go insane. The game is very entertaining, and well worth playing.
The game is a free download, see the link below. Its by default an ASCII based game. Before you yell at me for wasting your time, there are tilesets available that solve this issue.
To be honest the game has a ton of longevity to it, and is really fun as a play by email game. Typically each player plays a year, then mails the fort to the next person, who typically curses them for their shoddy work, and tries to get all the dead buried instead of lying all over the trade depot.
The game's official website is here.
The incredibly helpful wiki for this game is here.
You can get the newest version with a tile-set prepackaged here.