This weekend I stumbled upon a fantastic game called Dwarf Fortress.
The game is a management/city building game. First the game must randomly generate a persistent world that spans a very detailed 1000 years of history. You then take a bunch of dwarfs, find a mountain, start digging out your fortress and wait for your inevitable defeat.
The game has incredible depth, as you search for wealth in your mountain you must defend yourself from enemies, befriend civilizations, gather food, brew beer and train killers panda.
What I like about this game is that the developers have had the sole aim to make the game as deep and immersive as possible. I couldn’t possible list them all here but a comprehensive wiki can be found here.
..better upgrade that graphics card too: