Recs.
Updated
Open ended city-building simulator. Minecraft meets The Sims, with a difficulty level that can only be expressed through swear words.
Slaves to Armok: God of Blood Chapter II: Dwarf Fortress is a part roguelike, part city building game. It generates a high fantasy world using fractals and mathematical techniques so that each world is completely different. Like most roguelikes, Dwarf Fortress is text-based but don't think that means it's light on computer resources. DF is the most complicated and in depth game ever. Tarn and Zach Adams have worked on the game since 2002 and plan to work on it for another 20 years before it comes out of alpha.
SpecsUpdate
Pros
Pro Lots of ways to die, no ways to win
Starvation, riots, goblins raiders stealing your babies, goblin war parties stealing your lives, elephants, vampires, werewolves, werebears, werebadgers, carp, digging into an aquifer, digging into lava, digging into the nesting area of a Forgotten Beast, selling wood to hippies, insanity, drowning in knee-deep water, and being attacked by your own dismembered finger.
There are a lot of ways for dwarves to die. Age really isn't one ever heard of. After playing this game long enough, you'll realize why dwarves don't like going outside. Everything from harpies to dangerous man-eating carp is everywhere. Some of them are humorous, but most are a lesson.
The entire game acts as a massive learning experience. Don't tell your dwarves to fish; they don't know how to swim. Wall off your fortress or a necromancer will make your lunch attack you. Don't dig too far down, or something scary will follow you back up.
There is no victory, only glorious deaths. What goals you set in the game are up to you. Make small, simple goals that you know you can complete. "Surviving for 100 years" is like "curing cancer". Not technically 'impossible', but it might just be easier to settle on building a bridge for now.