There are casual games, and there are serious games.
Then there are hardcore games.
Then there are Nintendo hard games.
Somewhere beyond that, there's Dwarf Fortress.
Even if you don't intend to play the game (and we won't think any less of you if you don't), at least read the stories that have come from people who have played the game.
Holy Crap, explain this thing to me!
Dwarf Fortress is an expansive world simulation that goes into incredible detail. The programmers don't waste space/time on pretty pictures so they can get down to business!
You start by randomly generating a world. You can choose things like how many mountains there are, how tall the mountains are, how much fresh water and how much ocean, and if there's a fiery abyss full of demons at the core of the earth. Yes, I'm serious, and I advise you to turn that last one off if you don't like balrogs destroying everything.
From there you have your little band of randomly generated dwarves trying to make a settlement and survive. Look closely at each dwarf. They have names, hair colors, eye colors, likes, dislikes, skills, and more. Choose activities for each dwarf based on what you read. Have the strong ones dig your new home, have the smart ones build workshops and create things you need, the surly ones can become your military, and so on. You want these little guys to be happy or else they can go insane and kill each other.
Happy dwarves need alcohol, food, water, decent places to sleep, medical care, activities they enjoy, a militia for protection, and a little sunlight each day. And what do happy dwarves give back? Hours of entertainment! Watch as your dwarves grow, prosper, marry and have children. Send them on insane missions to build impossible structures of precious gems and gleaming metal. Watch them wage war on incoming invaders and snigger as you try hard not to offer the elves anything wooden or made from animals. Create the most epic empire of all time, then sit back and reap the glorious poems, histories, and art created by your loving people.
Oh wait, there is no sitting back here! Dwarf Fortress keeps going until all your dwarves are dead. From there you can send in a band of explorers to go Indiana Jones on your beautiful ruins as they witness firsthand what became of your people. Kill monsters, plunder treasure, and have an amazing time looting the world you created!
Yes, Dwarf Fortress is loaded with menus and has ASCII graphics.
The ASCII can be fixed with free mods made by players like you, so don't worry.
The menus are a needful evil as, without them, it would be even more impossible to take care of being basically god. Luckily, many menus have hotkeys. Write a cheat sheet out and stick it next to your computer so you can navigate easier.
Also, for the love of god, read the wiki. Don't just read during play, read before you start! This will prevent you from getting lost and having your dwarves be slaughtered by elves of all things within the first few hours of play. You can also learn tricks for making easier worlds, find free modifications, and gain a lot of strategic advice.
Only after you have read the wiki and played the game a little can you post in the forums. Doing otherwise makes you look like a retard, so for the love of god READ THE WIKI FIRST!
Now get out there and make the best Dwarven civilization ever!