If you don't know about the game, and like complex rpg-strategic games, with loads of dwarven fun, I highly recommend this game. With some patience (because the game is quite hard to get into, has a lot of stuff to do, which is a bit intimidating at first) this game has lots to offer.
The game has some influences from Dungeon Keeper, and other strategic games.
It's basically about constructing your fortress, and defending it against sieges. Before starting the game it generates a world map, you then choose a place to embark. You start with 7 dwarves with different skills (which you can choose if desired), and start digging into the mountains so your dwarves have a safe place to start construction of everything you will need; beds, food, booze, weapons, farms, glass furnaces, tables, chairs, leather-works, hospital, clothier, stupid things the damn nobles will ask for and many other stuff.
Once settled in you can start trading with human, dwarven and elven caravans for goods not available near your fortress (since there's different resources depending on where you embark). And getting ready a working military (arming them, training them), usually with the occasional immigrant with no skills, to fend off the inevitable raids goblins will wage on you, and other annoying pests like the gnolls.
Or the possible siege from a human or elven civilization that got mad with you. Elves are specially easier to anger, since they are hippies and get mad when you cut down too many trees >=(.
You can also set up all kind of traps, from the basics cage trap, stone-fall trap, weapon traps. To strategically opening a path of magma from your mountain to burn all your foes... and wildlife to hell.
With caged monsters you can have some fun setting up arenas or death labyrinths and watching them rip apart their limbs (the game has an amazing set-up on this, each living thing has limbs differentiated in-game, and internal organs, which can be pierced, bashed or cut-off in battle, leading to hilarious moments.)
The game offers ASCII graphics, or user-made tile-sets:
[Image: http://media.pcgamer.com/files/2010/08/dwarf-fortress-2.jpg]
[Image: http://media.pcgamer.com/files/2010/08/dwarf-fortress-4-mayday.jpg]
[Image: http://i.imgur.com/RcCu4.png]
And then there's the all wonderful stonsense to look around your fortress in an amazing isometric view.
[Image: http://media.pcgamer.com/files/2010/08/dwarf-fortress-5-stonesense.jpg]
The game has so many possibilities that amazing and fun stories from players are born every day.
So yeah, I highly recommend this game. There's some amazing tuts in case anyone's interesting in trying it out.
Dwarf Fortress Tutorials After Action Reporter
http://www.youtube.com/user/captnduck#grid/user/5A3D7682BDD48FC2
(Some stuff are a tad outdated in these tuts, but 90% of the info is still good. Exception being military, and the lack of hospital info, except in the written tut, which hospital info was added recently. And maybe one or another thingy, like magma, you can now find this in any map, by digging a lot of levels underground. Oh and captnduck, the guy that made the vidtuts, is making a new series with the new version, DF2010. Which already explains the new complex military system).