If you can look past the rough, rocky outside of Dwarf Fortress, you'll find a beautiful gem of gameplay.
Cited as main inspiration for Minecraft, Dwarf Fortress has many thing in common with it. In fact, you could describe it as a mix between Minecraft, Dungeon Keeper and The Sims, assuming by "Sims" you mean "short, drunk bearded men". It's also ridiculously complicated.
To start, you simply choose "Create World", set a few simple parameters and leave it be for a few seconds. Amazingly, instead of randomizing maps, this simulates a creation of a generic fantasy world, using tectonic movements, air pressure, temperature and many other factors to create a realistic world for you to play in. I'll have to warn you that even if you play for months, you'll never see more than 10% of it - worlds span hundreds of kilometers, while your fortress will be built on a tiny fraction of them. You can then choose a starting place for your humble, alcoholic civilization and set off.
You start the game as a band of seven settlers who arrive in a wagon at the site you chose. From there, you are free to do what you like - of course, assuming you like securing supplies for your dwarfs. Build bedrooms, craft merchandise and trade it for food with passing merchants, and you'll soon find your population growing as children are born and migrants arrive.
The game has no set goals. However, between goblin ambushes, monster sieges, occasional randomized giant, nigh-indestructible beasts that crawl out of the underworld, wars and dwarfs throwing tantrums prepare to fight for your fortresses survival more than you would like. The goal is to survive as long as you can.
And to survive, you have more tools than you could imagine. What would a dwarven fortress be with no traps? DF lets you use giant sawblades and axes, cages, falling rocks, arrows shooting out of nowhere, siege weapons and, worst of all, your own imagination to create an impenetrable defense. Of course, everything may eventually fail, so you'll want your military up and running as fast as you can. Yes, you can arm squads of highly trained dwarfs to teeth and send them to unleash hell on your attackers because, honestly, why not?
An aspect of Dwarf Fortress worth mentioning is the fanbase - if you ever run out of ideas you can simply go to bustling forums and browse other users creations. Maybe you'll learn how to build more effective fortifications? Maybe you'll get involved in a challenge to build a tower out of bars of soap?
Yes, Dwarf Fortress lets you build structures out of soap. Or any other one of hundreds of available materials. The game features at least ten different types of wood and hundreds of different stones and gems, differing in properties and value.
Soon, winter will come, which may either mean nothing, if you started in a warm climate, or freezing death, if you didn't. The games motto states "Losing is fun!". You'll need to acknowledge it, because Dwarf Fortress offers you no way to win, but infinite ways to lose. Goblin siege? Sure. Accidentally drowned the sleeping quarters with magma? Why not? Dug too deep and pierced the gate of hell? Yes, you can do that.
It's not long until you'll find yourself at 3AM, building complicated constructions out of retractable bridges, floodgates and magma. Or maybe you'd rather construct a beautiful village above ground, choosing usefulness over fortification?
Dwarf Fortress has no graphics and is notorious for being absurdly hard to play. However, it takes nothing more than downloading a texture pack for your fortress to stop being dots and letters and start being an overly complicated dwarven castle. Graphic packs are simple and offer little more than pictures of dwarfs and animals, but make Dwarf Fortress a lot easier to play. Prepare to not understand one or two aspects of building a fortress after many weeks of playing, yet prepare to have fun. Assuming, of course, that losing is fun.